Anatomy and Examination in Ocular Trauma

Ocular Trauma Series Editor: Hua Yan

Hua Yan Editor

Anatomy and Examination in Ocular Trauma

Ocular Trauma Series Editor: Hua Yan, Tianjin Medical University General Hospital, Tianjin, China

Ocular trauma can be a serious threat to vision, especially if not medically intervened appropriately and in a timely fashion. Immediate and accurate diagnosis and effective treatment is the key to save the eyes and visual function, as well as a great challenge to ophthalmologists, especially emergency doctors. This book series is designed to help the doctors and clinical practitioners have a thorough understanding of ophthalmic emergencies and a mastery of every details of ocular trauma. To do the best, it is required that the ER doctors have solid theoretical knowledge about the anatomy of the eye and basic skills in ophthalmic operations. For that reason, “Anatomy and examination of ocular trauma” is believed to be necessary and fundamental for this book series. Beyond this, familiarity with the emergency room and efficient protocol will be helpful for the doctors to give treatment in the first time, and it will also be an important part of this book series. Almost all the aspects and details of ocular trauma will be covered in this book series, including mechanical and non-mechanical ocular trauma. Special topics of complicated situations, such as ciliary body impairment, will also be introduced in this book series. Hopefully the readers will enjoy it and find it helpful for them to provide better care to the patients and save vision. More information about this series at http://www.springer.com/series/15621

Hua Yan Editor

Anatomy and Examination in Ocular Trauma

Editor Hua Yan Department of Ophthalmology Tianjin Medical University General Hospital Tianjin, China

ISSN 2523-3157     ISSN 2523-3165 (electronic) Ocular Trauma ISBN 978-981-13-0067-7    ISBN 978-981-13-0068-4 (eBook) https://doi.org/10.1007/978-981-13-0068-4 Library of Congress Control Number: 2018956413 © Springer Nature Singapore Pte Ltd. 2019 This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, express or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Singapore Pte Ltd. The registered company address is: 152 Beach Road, #21-01/04 Gateway East, Singapore 189721, Singapore

Acknowledgments

Dr. Yan extends his sincere thanks to the doctors in the field of ocular trauma around the world. Special thanks go to Dr. Yuanpei Zheng, Dr. Mengyu Liao, and Dr. Xinlei Zhu for providing precious visual field photos; Dr. Hanqiao Zhang and Dr. Shancheng Si for providing photos for the “Physical Examination”; and Dr. Pablo Grigera for providing the UBM pictures.

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Contents

Part I Anatomy 1 General Anatomy ��������������������������������������������������������������������������    3 Kang Feng, Caiyun You, and Ling Yuan 2 Ocular Structure Change and Specific Feature When Encountered with Trauma and Pearls������������������������������   31 Hua Yan, Caiyun You, and Ling Yuan Part II Examinations 3 Visual Function Examination ������������������������������������������������������   39 Yun Feng and Baoqun Yao 4 Physical Examination��������������������������������������������������������������������   67 Yuntao Hu and Qihua Wang 5 Imaging Examination��������������������������������������������������������������������   81 Andrés M. Rousselot, Jing Zhang, and Huaigui Liu Part III Epidemiology and the Registration System of Ocular Trauma 6 Epidemiology of Ocular Trauma��������������������������������������������������  105 Kang Feng 7 The Registration System of Ocular Trauma��������������������������������  123 Kang Feng

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Part I Anatomy

1

General Anatomy Kang Feng, Caiyun You, and Ling Yuan

Abstract

A thorough understanding of the anatomy of the eyeball and the traumatic characteristics of each structure of the eyeball are a prerequisite for proper interpretation of long-term outcomes of mechanical eye injuries. Furthermore, such anatomic knowledge is essential to the proper planning and safe execution of globe exploration and vitreoretinal surgery. Whereas most knowledge of these matters is based on anatomic dissections, either postmortem or during surgery, noninvasive techniques particularly magnetic resonance imaging (MRI), ultrasonography, and optical coherence tomography (OCT) are increasingly providing additional information. Keywords

Cornea · Sclera · Retina · Choroid · Macula

K. Feng (*) Department of Ophthalmology, Peking University Third Hospital, Beijing, China e-mail: [email protected] C. You (*) Department of Ophthalmology, Tianjin Medical University General Hospital, Tianjin, China L. Yuan (*) Department of Ophthalmology, First Affiliated Hospital of Kunming Medical University, Yunnan, China e-mail: [email protected]

1.1

Anatomy of the Eyeball

Kang Feng

1.1.1 The Eyeball The normal adult globe is approximately spherical, with an anteroposterior diameter of the adult eye being approximately 23–25  mm (Fig.  1.1). Myopic eyes tend to be longer, and hyperopic eyes tend to be shorter. The radius of curvature of the cornea (8  mm) is smaller than that of the sclera (12 mm), making the shape of the globe an oblate spheroid (Fig. 1.2). The eyeball includes eyeball wall and eye contents. The outer wall of the eyeball is composed of three concentric layers. The outermost layer consists of the clear cornea anteriorly and the opaque white sclera posteriorly. The outermost corneoscleral layer is composed of tough and protective tissues. The middle is uvea and inner is retina. Other important surface features of the globe, such as the vortex veins, the posterior ciliary artery and nerves, extraocular muscle insertions, and the optic nerve and its surrounding meningeal sheaths, are discussed in other chapters. The intraocular space contains three compartments: the anterior chamber, the posterior chamber, and the vitreous cavity. The anterior chamber, the space between the iris and the cornea, is filled

© Springer Nature Singapore Pte Ltd. 2019 H. Yan (ed.), Anatomy and Examination in Ocular Trauma, Ocular Trauma, https://doi.org/10.1007/978-981-13-0068-4_1

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K. Feng et al.

4 Cornea

a

Iris Ciliary body Conjunctiva Sclera Choroid Retina

b Canal of schlemm

Pupil

Cornea Iris

Conjunctiva Ciliary body

Anterior chamber angle

Pars plicata

Episcleral veins

Pars plana

Posterior chamber Zonule

Lateral rectus muscle

Medial rectus muscle Lens capsule

Lens Choroid

Ora serrata Retina Choroid

Vortex vein

Sclera Vitreous

Retina Macula

Retinal pigment epithelium

Long ciliary artery and ciliary nerve

Retinal arteriles and veins

Optic disk Dura Pia

Lamina cribrosa Arachnoid Optic nerve Central retinal artery and vein

Fig. 1.1 (a) Layers of the globe (Adapted from [1]). (b) Internal structures of the human eye. (Adapted from [2])

1  General Anatomy

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EQUATOR ORA SERRATA

VORTEX VEIN

POSTERIOR POLE

Fig. 1.2  Profile of eyeball and several major cross sections. (Simulated diagram)

with aqueous fluid. It is about 3 mm deep, with an average volume of 0.25 mL. The posterior chamber is the anatomical portion of the eye posterior to the iris and anterior to the lens and vitreous face. It is also filled with aqueous fluid and has an average volume of 0.06 mL. The largest compartment of the eye is the vitreous cavity, which makes up four-fifths of the volume of the eye (4.0 mL) and contains the vitreous gel. The total volume of the average adult eye is approximately 6.5–7 mL.

1.1.2 The Cornea The cornea occupies the center of the anterior pole of the globe. Because the sclera and conjunctiva overlap the cornea anteriorly, the cornea appears elliptical when viewed from the front. In the adult, it measures about 12 mm in the horizontal meridian and about 11  mm in the vertical. From behind, when the cornea is viewed at its posterior landmark (the Schwalbe’s line-the termination of Descemet’s membrane), its circumference appears circular. The cornea is inserted into the sclera at the limbus, the circumferential depression at this junction being known as the scleral sulcus. The average adult cornea is 0.5 mm thick in the center, and 1 mm thick in the margin.

Sources of nutrition for the cornea are the vessels of the limbus, the aqueous, and the tears. The superficial cornea also gets most of its oxygen from the atmosphere. The sensory nerves of the cornea are supplied by the first (ophthalmic) division of the fifth (trigeminal) cranial nerve. The transparency of the cornea is due to its uniform structure, avascularity, and deturgescence. Once the cornea is injured, it will affect the refractive state of it. From anterior to posterior, it has five distinct layers (Fig.  1.3): the epithelium (which is continuous with the epithelium of the bulbar conjunctiva), Bowman’s layer, the stroma, Descemet’s membrane, and the endothelium. The epithelium has five or six layers of cells. Nonepithelial cells may appear within the corneal epithelial layer. Wandering histiocytes, macrophages, lymphocytes, and pigmented melanocytes are frequent components of the peripheral cornea. Antigen-presenting Langerhans cells are found peripherally and move centrally with age or in response to keratitis. The cornea is often traumatized as it is exposed to the surface. Any damage to the corneal epithelium can cause severe pain, but some cases feel no pain in severe chemical injury that make the cornea loss of feeling. The occasional recurrence corneal erosion will occur following a trauma. Diffuse damage to the limbal stem cells, especially by chemical burns, leads to chronic epithelial surface defects. Beneath the basal lamina is Bowman’s layer, or Bowman’s membrane, a tough layer consisting of randomly dispersed collagen fibrils. It is a modified region of the anterior stroma. Bowman’s membrane is more resistant to mechanical damage, but weak to chemical damage. Unlike Descemet’s membrane, it is not restored after injury but is replaced by scar tissue. So the damage to the Bowman’s membrane leads to opacity of the cornea. The stroma constitutes approximately 90% of the total corneal thickness in humans. It is composed of collagen-producing keratocytes, ground

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Fig. 1.3 Transverse section of cornea. (Adapted from [1])

Epithelium Bowman’s membrane

Stroma

Descemats membrane Endothelium

substance, and collagen lamellae. The collagen fibrils form obliquely oriented lamellae in the anterior third of the stroma (with some interlacing) and parallel lamellae in the posterior two-­ thirds. The corneal collagen fibrils extend across the entire diameter of the cornea, finally winding circumferentially around the limbus. The fibrils are remarkably uniform in size and separation, and this regularity helps determine the transparency of the cornea. Any damage to the corneal stroma will make the cornea opaque. The basal lamina of the corneal endothelium, Descemet’s membrane, is a true basement membrane, and its thickness increases with age. At birth, it is 3–4  μm thick; thickness increases throughout life to an adult level of 8–10  μm. Opposite to Bowman’s membrane, Descemet’s membrane is more resistant to chemical and pathological damage, but weak to mechanical

damage. Descemet’s membrane is not tightly connected to the stroma and the endothelium, so it is easily detached following trauma. The corneal endothelium is composed of a single layer of mostly hexagonal cells derived from the neural crest, but this is responsible for maintaining the essential deturgescence of the corneal stroma. Approximately 500,000 cells are present, with a density of about 3000 cells/mm2. The size, shape, and morphology of the endothelial cells can be observed by specular microscopy at the slit lamp. The apical surfaces of these cells face the anterior chamber; their basal surfaces about Descemet’s membrane. Typically, young endothelial cells have a large nucleus and abundant mitochondria. The active transport of ions by these cells leads to the transfer of water from the corneal stroma and the maintenance of stromal deturgescence and transparency. In humans,

1  General Anatomy

endothelial mitosis is limited, and the overall number of endothelial cells decreases with age. The endothelium is quite susceptible to injury as well as undergoing loss of cells with age. Endothelial repair is limited to enlargement and sliding of existing cells, with little capacity for cell division. Failure of endothelial function leads to endothelial decompensation, stromal edema, and visual failure.

1.1.3 The Sclera The sclera is the fibrous outer protective coating of the eye, consisting almost entirely of collagen. The sclera covers the posterior four-fifths of the surface of the globe, with an anterior opening for the cornea and a posterior opening for the optic nerve. The tendons of the rectus muscles insert into the superficial scleral collagen. The Tenon capsule covers the sclera and rectus muscles anteriorly, and both are overlain by the bulbar conjunctiva. The capsule and conjunctiva fuse near the limbus. In contrast to the transparent cornea, the sclera is opaque and white. It is 0.4–0.5 mm thick at the equator and 0.6 mm thick anterior to the muscle insertions. Thinnest just behind the insertions of the rectus muscles (0.3 mm), the scleral increases to approximately 1  mm thick posteriorly but becomes thin at the lamina cribrosa, where the axons of the ganglion cells exit to form the optic nerve. Because of the thinness of the sclera, strabismus and retinal detachment surgery require careful placement of sutures. Scleral rupture following blunt trauma can occur at a number of sites: in a circumferential arc parallel to the corneal limbus opposite the site of impact, at the insertion of the rectus muscles, or at the equator of the globe. So it is easy to tear from the muscle insertion point, when the eye is subjected to external force. The sclera, like the cornea, is essentially avascular except for the superficial vessels of the episclera and the intrascleral vascular plexus located just posterior to the limbus. A number of channels, or emissaria, penetrate the sclera, allowing for the passage of arteries, veins, and nerves.

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Extraocular extension of malignant melanoma of the choroid often occurs by way of the emissaria. Branches of the ciliary nerves that supply the cornea sometimes leave the sclera to form loops posterior to the nasal and temporal limbus. Anteriorly, the episclera consists of a dense vascular connective tissue that merges deeply with the superficial sclera and superficially with the Tenon capsule and the conjunctiva. The scleral stroma is composed of bundles of collagen, fibroblasts, and a moderate amount of ground substance. Across the posterior scleral foramen are bands of collagen and elastic tissue, forming the lamina cribrosa. Around the optic nerve, the sclera is penetrated by the long and short posterior ciliary arteries and the long and short ciliary nerves. The long posterior ciliary arteries and long ciliary nerves pass from the optic nerve to the ciliary body in a shallow groove on the inner surface of the sclera at the 3 and 9 o’clock meridians. Slightly posterior to the equator, the four vortex veins draining the choroid exit through the sclera, usually one in each quadrant. About 4 mm posterior to the limbus, slightly anterior to the insertion of the respective rectus muscle, the four anterior ciliary arteries and veins penetrate the sclera. The nerve supply to the sclera is from the ciliary nerves. Lacerations due to contusion trauma sometimes cause lamellar lacerations of sclera, which is difficult to suture.

1.1.4 The Uveal Tract The middle layer of the globe is the uvea, which consists of the choroid, ciliary body, and iris. Highly vascular, it serves a nutritive and supportive function and is protected by the cornea and sclera. The uveal tract is the main vascular compartment of the eye. It consists of three parts: iris, ciliary body (located in the anterior uvea), and choroid (located in the posterior uvea). The uveal tract is firmly attached to the sclera at only three sites: the scleral spur, the exit points of the vortex veins, and the optic nerve. These attachments account for the characteristic anterior balloons formed in choroidal detachment.

K. Feng et al.

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1.1.5 Iris The iris is the anterior extension of the ciliary body. The iris is the most anterior extension of the uveal tract. It is made up of blood vessels and connective tissue, in addition to the melanocytes and pigment cells that are responsible for its distinctive color. Differences in color are related to the amount of pigmentation in the anterior border layer and the deep stroma. It presents as a flat surface with a centrally situated round aperture, the pupil. The iris lies in contiguity with the anterior surface of the lens, dividing the anterior chamber from the posterior chamber, each of which contains aqueous humor. Within the stroma of the iris are the sphincter and dilator muscles. The two heavily pigmented layers on the posterior surface of the iris represent anterior extensions of the neuroretina and retinal pigment epithelium. The blood supply to the iris is from the major circle of the iris. Iris capillaries have a nonfenestrated endothelium and hence do not normally leak intravenously injected fluorescein. Blood vessels form the bulk of the iris stroma. Most follow a radial course, arising from the major arterial circle and passing to the center of the pupil. Anastomoses occur between the arterial and venous arcades to form the minor vascular circle of the iris, which is often incomplete. The major arterial circle is located at the apex of the ciliary body, not the iris. In humans, the anterior border layer is normally avascular. The posterior surface of the iris is densely pigmented and appears velvety smooth and uniform. It is continuous with the nonpigmented epithelium of the ciliary body and with the neurosensory portion of the retina. Sensory nerve supply to the iris is via fibers in the ciliary nerves. The iris controls the amount of light entering the eye. Pupillary size is principally determined by a balance between constriction due to parasympathetic activity transmitted via the third cranial nerve and dilation due to sympathetic activity. There is dual sympathetic and parasympathetic innervation. Interruption of the sympathetic nerve supply due to orbital fracture results in Horner syndrome, with miosis, in addition to

ptosis and anhydrosis. Like the dilator muscle, the sphincter muscle is derived from neuroectoderm. It is composed of a circular band of smooth muscle fibers and is located near the pupillary margin in the deep stroma, anterior to the pigment epithelium of the iris. The reciprocal sympathetic innervation to the sphincter appears to serve an inhibitory role, helping to relax the sphincter in darkness. Iris is prone to iridodialysis following contusion.

1.1.6 The Ciliary Body The ciliary body, roughly triangular in cross section, extends forward from the anterior end of the choroid to the root of the iris (about 6  mm). It consists of a corrugated anterior zone, the pars plicata (2 mm), and a flattened posterior zone, the pars plana (4  mm). The ciliary processes arise from the pars plicata. The only attachment of the ciliary body to the sclera is at its base, via its longitudinal muscle fibers, where they insert into the scleral spur (Fig. 1.4). The ciliary body has two principal functions: aqueous humor formation and lens accommodation. They are composed mainly of capillaries and veins that drain through the vortex veins. The capillaries are large and fenestrated and hence leak intravenously injected fluorescein. There are two layers of ciliary epithelium: an internal nonpigmented layer, representing the anterior extension of the neuroretina, and an external pigmented layer, representing an extension of the retinal pigment epithelium. The ciliary processes and their covering ciliary epithelium are responsible for the formation of aqueous. The ciliary body detachment or cyclodialysis and detachment of epithelium of ciliary body can occur due to trauma [4]. The ciliary muscle is composed of a combination of longitudinal, circular, and radial fibers. The function of the circular fibers is to contract and relax the zonular fibers, which originate in the valleys between the ciliary processes. This alters the tension on the capsule of the lens, giving the lens a variable focus for both near and distant objects in the visual field. Most of the ciliary muscles are made up of an outer layer of lon-

1  General Anatomy Fig. 1.4  Inner surface of ciliary body. 1. Pars plicata, 2. choroid, 3. zonuler, 4. lens, 5. sclera, 6. pars plicata, 7. ciliary process, 8. inner face of iris, 9. ora serrate, 10. retina, 11. pars plana. (Adapted from [3])

9 1. Pars plicata 2. Choroid 3. Zonuler 11. Pars plana

4. Lens 5. Sclera

10. Retina

9. Ora serrate

6. Pars plicata

7. Ciliary process 8. Inner face of iris

gitudinal fibers that attach to the scleral spur. The longitudinal fibers insert into the trabecular meshwork to influence its pore size. The radial muscle fibers arise in the midportion of the ciliary body, and the circular fibers are located in the innermost portion. Clinically the three groups of muscle fibers function as a unit. Presbyopia is associated with age-related changes in the lens rather than to changes in the ciliary muscle. Even so, the muscle does change with age, with increasing amounts of connective tissue between the muscle bundles and a loss of elastic recoil after contraction. Both myelinated and nonmyelinated nerve fibers are observed throughout the ciliary muscle. Innervation is mainly derived from parasympathetic fibers via the short ciliary nerves. Sympathetic fibers have also been observed which may play a role in relaxing the muscle. Cholinergic drugs contract the ciliary muscle. Because some of the muscle fibers form tendinous attachments to the scleral spur, their contraction increases aqueous flow by opening up the spaces of the trabecular meshwork. The blood vessels supplying the ciliary body are derived from the major circle of the iris (Fig. 1.5). The sensory nerve supply of the iris is via the ciliary nerves. The capillary plexus of each ciliary process is supplied by arterioles as they pass anteriorly and posteriorly from the major arterial circle; each plexus is drained by 1 or 2 large venules located at the crest of each pro-

cess. Sphincter tone within the arteriolar smooth muscle affects the capillary hydrostatic pressure gradient. In addition, it influences whether blood flows into the capillary plexus or directly to the draining choroidal vein, bypassing the plexus completely. Neuronal innervation of the vascular smooth muscle and humoral vasoactive substances may be important in determining regional blood flow, capillary surface area available for exchange of fluid, and hydrostatic capillary pressure. All of these affect the rate of aqueous humor formation. The ciliary body is lined by a double layer of epithelial cells, the nonpigmented and the pigmented epithelium. The inner, nonpigmented epithelium is located between the aqueous humor of the posterior chamber and the outer pigmented epithelium. The basal surface of the nonpigmented epithelium, which borders the posterior chamber, is covered by the basal lamina, which is multilaminar in the valleys of the processes. The basal lamina of the pigmented epithelium which faces the iris stroma is thick and more homogeneous than that of the nonpigmented epithelium. The uveal portion of the ciliary body consists of comparatively large fenestrated capillaries, collagen fibrils, and fibroblasts. The main arterial supply to the ciliary body comes from the anterior and the long posterior ciliary arteries which join together to form a multilayered arterial plexus consisting of a superficial episcleral plexus, a deeper intramuscular plexus, and an incomplete major arterial circle

K. Feng et al.

10 Fig. 1.5  Anterior vessel and innervation of uveal tract. 1. Minor iridis arterial circle, 2. iris pupil margin, 3. major arterial circle, 4. long ciliary nerves, 5. choroid, 6. iris ciliary margin. (Adapted from [3])

1. Minor iridis arterial circle

2. Iris pupil margin 6. Iris ciliary margin

5. Choroid 3. Major arterial circle

4. Long ciliary nerves

often mistakenly attributed to the iris but actually located posterior to the anterior chamber angle recess in the ciliary body. The major veins drain posteriorly through the vortex system although some drainage also occurs through the ­intrascleral venous plexus and the episcleral veins into the limbal region.

1.1.7 The Choroid The choroid is the posterior segment of the uveal tract, between the retina and the sclera, and nourishes the outer portion of the retina (Fig.  1.6). It averages 0.25 mm in thickness and consists of three layers of vessels: the choriocapillaris, which is the innermost layer, a middle layer of small vessels, and an outer layer of large vessels. The deeper the vessels are placed in the choroid, the wider their lumens. Blood from the choroidal vessels drains via the four vortex veins, one in each of the four posterior quadrants. The choroid is bounded internally by Bruch’s membrane and externally by the sclera. The suprachoroidal space lies between the choroid and the sclera. The choroid is firmly attached posteriorly to the margins of the optic nerve. Anteriorly, the choroid joins with the ciliary body. Severe injury to

the eyeball can result in the laceration of vortex which is the cause of expulsive suprachoroidal hemorrhage. Perfusion of the choroid comes from both the long and the short posterior ciliary arteries and from the perforating anterior ciliary arteries. Blood flow through the choroid is high compared to that of other tissues. As a result, the oxygen content of choroidal venous blood is only 2–3% less than that of arterial blood. Bruch’s membrane is a basal laminae of the retinal pigment epithelium (RPE) and the choriocapillaris of the choroid. It extends from the margin of the optic disc to the ora serrata, and ultrastructurally it has five elements: the basal lamina of the RPE; inner collagenous zone; thicker porous band of elastic fibers, middle layer of elastic fibers; outer collagenous zone; and basement membrane of the endothelium of the choriocapillaris. Bruch’s membrane, therefore, consists of a series of connective tissue sheets that are highly permeable to small molecules such as fluorescein. Defects in Bruch’s membrane develop spontaneously in myopia or pseudoxanthoma elasticum or they result from trauma or inflammation. Subretinal neovascular membranes can arise as a result of these defects. And they can lead to disciform macular changes as part of exudative age-related macular degeneration.

1  General Anatomy

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a Ganglion cells

Bipolar cells

Rods and cones Pigment epithelium Choroid Pigment epithelium

Small choroidal vessels (choriocapillaries)

b Bruch’s membrane

Large choroidal vessels

Suprachoroid

Sclera

Fig. 1.6 (a) The retina and choroid. (Adapted from [1]). (b) Cross section of choroid. (Adapted from [2])

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The vessel walls of choriocapillaris are extremely thin and contain multiple fenestrations especially on the surface facing the retina. Pericytes are located along the outer wall. The middle and outer choroidal vessels are not fenestrated. The large vessels typical of small arteries elsewhere possess an internal elastic lamina and smooth muscle cells in the media. As a result, small molecules such as fluorescein, which diffuse across the endothelium of the choriocapillaris, do not leak through medium and large choroidal vessels. Abundant melanocytes as well as occasional macrophages, lymphocytes, mast cells, and plasma cells appear throughout the choroidal stroma. The intercellular space contains collagen fibers and nerve fibers. In lightly pigmented eyes, pigmentation in the choroid is sparse compared with that of darkly pigmented eyes. The degree of pigmentation in the choroid must be considered when one is performing photocoagulation because it influences the absorption of laser energy.

1.1.8 The Retina The innermost layer of the globe is the retina. This photosensitive layer contains the photoreceptors and neural elements that initiate the processing of visual information (Fig. 1.7). The retina is a thin, semitransparent, multilayered sheet of neural tissue that lines the inner aspect of the posterior two-thirds of the wall of

Fig. 1.7  The fundus photo of normal eyeball

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the globe. It extends almost as far anteriorly as the ciliary body, ending at that point in a ragged edge, the ora serrata. The outer surface of the sensory retina is apposed to the retinal pigment epithelium and thus related to Bruch’s membrane, the choroid, and the sclera. In most areas, the retina and retinal pigment epithelium are easily separated to form the subretinal space, such as that occurs in retinal detachment. But at the optic disk and the ora serrata, the retina and retinal pigment epithelium are firmly bound together, thus limiting the spread of subretinal fluid in retinal detachment. This contrasts with the potential suprachoroidal space between the choroid and sclera, which extends to the scleral spur. Choroidal detachments thus extend beyond the ora serrata, under the pars plana and pars plicata. The epithelial layers of the inner surface of the ciliary body and the posterior surface of the iris represent anterior extensions of the retina and retinal pigment epithelium. The inner surface of the retina is apposed to the vitreous. The fundus oculi is the part of the eye that is visible on ophthalmoscopy, including the retina and its vessels and the optic nerve head (or optic disc). The macula, 5–6  mm in diameter, lies between the temporal vascular arcades. At the macula’s center lies the fovea, rich in cones and responsible for color vision and the highest visual acuity. In the far periphery, the ora serrata (the junction between the retina and the pars plana) can be seen by gonioscopy or indirect ophthalmoscopy. The reddish color of the fundus is due to the transmission of light reflected from the posterior sclera through the capillary bed of the choroid. In cross section, from inner to outer retina, its layers are as follows: (1) internal limiting membrane (ILM); (2) nerve fiber layer (NFL), containing the ganglion cell axons passing to the optic nerve; (3) ganglion cell layer (GCL); (4) inner plexiform layer (IPL), containing the connections of the ganglion cells with the amacrine and bipolar cells; (5) inner nuclear layer (INL) of bipolar amacrine, and horizontal cell bodies; (6) middle limiting membrane (MLM); (7) outer plexiform layer (OPL), containing the connections of the bipolar and horizontal cells with the photorecep-

1  General Anatomy

tors; (8) outer nuclear layer of photoreceptor cell nuclei (ONL); (9) external limiting membrane (XLM); (10) photoreceptor layer of rod and cone inner and outer segments (IS/OS); and (11) retinal pigment epithelium. The inner layer of Bruch’s membrane is actually the basement membrane of the retinal pigment epithelium. The retina is 0.1  mm thick at the ora serrata and 0.56 mm thick at the posterior pole. The retina receives its blood supply from two sources: the choriocapillaris immediately outside Bruch’s membrane, which supplies the outer third of the retina, including the outer plexiform and outer nuclear layers, the photoreceptors, and the retinal pigment epithelium; and branches of the central retinal artery, which supply the inner two-thirds. The fovea is supplied entirely by the choriocapillaris and is susceptible to irreparable damage when the retina is detached. The retinal blood vessels have a nonfenestrated endothelium, which forms the inner blood–retinal barrier. The endothelium of choroidal vessels is fenestrated. The outer blood–retinal barrier lies at the level of the retinal pigment epithelium. The structure of the outer pigmented epithelial layer is relatively simple compared with that of the overlying inner, or neurosensory, retina. The RPE consists of a monolayer of hexagonal cells that extends anteriorly from the optic disc to the ora serrata, where it merges with the pigmented epithelium of the ciliary body. Its structure is deceptively simple considering its many functions: vitamin A metabolism, maintenance of the outer blood–retina barrier, phagocytosis of the photoreceptor outer segments, absorption of light (reduction of scatter), heat exchange, formation of the basal lamina, production of the mucopolysaccharide matrix surrounding the outer segments, and active transport of materials in and out of the RPE.  Like other epithelial and endothelial cells, the RPE cells are polarized. The basal aspect is intricately folded and provides a large surface of attachment to the thin basal lamina that forms the inner layer of Bruch’s membrane. The apices have multiple villous processes that engage with the photoreceptor outer segments, embedded in a mucopolysaccharide matrix (interphotoreceptor matrix) containing

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chondroitin-6-sulfate, sialic acid, and hyaluronic acid. Separation of the RPE from the neurosensory retina is called retinal detachment, which can occur in trauma cases. The cytoplasm of the RPE also contains numerous mitochondria (involved in aerobic metabolism), rough-surfaced endoplasmic reticulum, a Golgi apparatus, and a large round nucleus. Throughout life, incompletely digested residual bodies, lipofuscin pigment, phagosomes, and other materials are excreted beneath the basal lamina of the RPE. These contribute to the formation of drusen, which are accumulations of this extracellular material. They can vary in size and are commonly classified by their funduscopic appearance as either hard or soft drusen. They are typically located between the basement membrane of the RPE cells and the inner collagenous zone of Bruch’s membrane. RPE seldom were affected by trauma, and in some cases RPE disappeared due to injury. The neurosensory retina is composed of neuronal, glial, and vascular elements. The photoreceptor layer of the neurosensory retina consists of highly specialized neuroepithelial cells called rods and cones. Each photoreceptor cell consists of an outer and an inner segment. The outer segments, surrounded by a mucopolysaccharide matrix, make contact with the apical processes of the RPE. Tight junctions or other intercellular connections do not exist between the photoreceptor cell outer segments and the RPE.  The factors responsible for keeping these layers in apposition are poorly understood but probably involve active transport. The rod photoreceptor consists of an outer segment that contains multiple laminated discs resembling a stack of coins and a central connecting cilium. The rod inner segment is subdivided into two additional elements: an outer ellipsoid containing a large number of mitochondria and an inner myoid containing a large amount of glycogen; the myoid is continuous with the main cell body, where the nucleus is located. The inner portion of the cell contains the synaptic body, or spherule, of the rod, which is formed by a single invagination that accommodates two horizontal cell processes and one or more central bipolar dendrites.

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The cone synaptic body, or pedicle, is more complex than the rod spherule. The outer segments of the cones have a different morphology depending on their location in the retina. The extrafoveal cone photoreceptors of the retina have conical ellipsoids and myoids, and their nuclei tend to be closer to the external limiting membrane than are the nuclei of the rods. Cone pedicles synapse with other rods and cones as well as with horizontal and bipolar cell processes. Horizontal cells make synaptic connections with many rod spherules and cone pedicles; they also extend cell processes horizontally throughout the outer plexiform layer. Bipolar cells are oriented vertically. Their dendrites synapse with either rod or cone synaptic bodies, and their axons make synaptic contact with ganglion cells and amacrine cells in the inner plexiform layer. The axons of the ganglion cells bend to become parallel to the inner surface of the retina, where they form the nerve fiber layer and later the axons of the optic nerve. Each optic nerve has more than one million optic nerve fibers. The nerve fibers from the temporal retina follow an arcuate course around the macula to enter the superior and inferior poles of the optic disc. The papillomacular fibers travel straight to the optic nerve from the fovea. The nasal axons also pursue a radial course. The visibility of the nerve fibers is enhanced when they are viewed ophthalmoscopically using green (red-free) illumination. The neuronal elements and their connections in the retina are highly complex. Many types of bipolar, amacrine, and ganglion cells exist. The neuronal elements of more than 120 million rods and 6 million cones are interconnected, and signal processing within the neurosensory retina is significant. Muller cells are glial cells that extend vertically from the external limiting membrane inward to the internal limiting membrane. Their nuclei are located in the inner nuclear layer. Muller cells, along with the other glial elements (the fibrous and protoplasmic astrocytes and microglia), provide structural support and nutrition to the retina. The retinal blood vessels are analogous to the cerebral blood vessels and maintain the inner blood–retina barrier. This physiologic barrier is

due to the single layer of nonfenestrated endothelial cells, whose tight junctions are impervious to tracer substances such as fluorescein and horseradish peroxidase. Muller cells and other glial elements are generally attached to the basal lamina of retinal blood vessels. Retinal blood vessels lack an internal elastic lamina and the continuous layer of smooth muscle cells found in other vessels in the body. Smooth muscle cells are occasionally present in vessels near the optic nerve head. They become a more discontinuous layer as the retinal arterioles pass farther out to the peripheral retina. The retinal blood vessels do not ordinarily extend deeper than the middle limiting membrane. Where venules and arterioles cross, they share a common basement membrane. Venous occlusive disorders are common at an arteriovenous crossing. The inner portion of the retina is perfused by branches of the central retinal artery. In 30% of eyes and 50% of people, a cilioretinal artery, branching from the ciliary circulation, also supplies part of the inner retina. Overall, cells and their processes in the retina are oriented perpendicular to the plane of the RPE in the middle and outer layers but parallel to the retinal surface in the inner layers. For this reason, deposits of blood or exudates tend to form round blots in the outer layers (where small capillaries are found) and linear or flame-shaped patterns in the nerve fiber layer. At the fovea, the outer layers also tend to be parallel to the surface (Henle fiber layer). As a result, radial or star-­ shaped patterns may arise when these extracellular spaces are filled with serum and exudate.

1.1.9 Macula The terms macula, macula lutea, posterior pole, area centralis, fovea, and foveola have created confusion among anatomists and clinicians. Clinical retina specialists tend to regard the macula as the area of 5.5–6.0 mm diameter in the center of the posterior retina bounded by the temporal retinal vascular arcades. It is known to anatomists as the area centralis, being defined histologically as that part of the retina in which the ganglion cell layer is more than one cell thick (Fig. 1.8).

1  General Anatomy

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1.75mm

Foveolar 0.35mm Umbo 0.15mm Parafovea 0.5mm Perifovea 1.5mm

Fovea 1.5mm 2.5mm Macular 5.5mm

1.5mm

1.5mm

7.0 - 8.0 mm

Near periphery

Fig. 1.8  Macular (Simulated diagram)

The name macula lutea (“yellow spot”) is derived from the yellow color of the central retina; this color is due to the presence of carotenoid pigments and yellow luteal pigment xanthophyll, chiefly located in the Henle fiber layer. Two major pigments have been identified—zeaxanthin and lutein—whose proportions vary with distance from the fovea: the lutein-to-zeaxanthin ratio is 1:2.4 in the central area (0.25 mm from the fovea) and greater than 2:1 in the periphery (2.2–8.7  mm from the fovea). This variation in pigment ratio corresponds to the rod-to-cone ratio. Lutein is more concentrated in rod-dense areas of the retina; zeaxanthin is more concentrated in cone-dense areas. Lipofuscin, the yellow

age pigment, has been observed in the cytoplasm of the perifoveal ganglion cells by electron microscopy. The fovea corresponds to the retinal avascular zone of fluorescein angiography and is characterized by thinning of the outer nuclear layer and absence of the other parenchymal layers as a result of the oblique course of the photoreceptor cell axons (Henle fiber layer) and the centrifugal displacement of the retinal layers that are closer to the inner retinal surface. In the center of the macula, 4 mm lateral to the optic disk and 0.8 mm inferior to the center of the optic disc, is the 0.25-mm-diameter foveola, clinically obvious as a depression that creates a particular reflection when viewed ophthalmoscopically.

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It is the thinnest part of area of the retina (0.25 mm), containing only cone photoreceptors. The histologic features of the fovea and foveola provide for fine visual discrimination, the foveola providing optimal visual acuity. The normally empty extracellular space of the retina is potentially greatest at the macula. Diseases that lead to accumulation of extracellular material particularly cause thickening of this area (macular edema). Contusion usually resulted in the macular edema or macular hole which is a full-thickness laceration of sensory retina. The photoreceptor layer of the foveola is made up entirely of cones, whose close packing accounts for the high visual acuity for which this small area is responsible. The foveal cones are shaped like rods but possess all the cytologic characteristics of extramacular cones. The outer segments are oriented parallel to the visual axis and perpendicular to the plane of the RPE. In contrast, the peripheral photoreceptor cell outer segments are tilted toward the entrance pupil. The fovea is a concave central retinal depression approximately 1.5 mm in diameter; it is comparable in size to the optic nerve head. Its margins are clinically inexact, but in younger subjects the fovea is evident ophthalmoscopically as an elliptical light reflex that arises from the slope of the thickened ILM of the retina. From this point inward, the basal lamina rapidly decreases in thickness as it dives down the slopes of the fovea toward the depths of the foveola, where it is barely visible, even by electron microscopy. Around the fovea is the parafovea, 0.5  mm wide, where the GEL, the INL, and the OPL are thickest; surrounding this zone is the most peripheral region of the macula, the perifovea, 1.5 mm wide. The masking of choroidal fluorescence observed in the macula during fundus fluorescein angiography is caused partly by xanthophyll pigment and partly by the higher melanin pigment content of the foveal RPE.

1.1.10 Ora Serrata The ora serrata is the boundary between the retina and the pars plana. Its distance from the Schwalbe’s line is between 5.75 mm nasally and

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6.50 mm temporally. In myopia, this distance is greater; in hyperopia, it is shorter. Bruch’s membrane extends anteriorly, beyond the ora serrate, but is modified because there is no choriocapillaris in the ciliary body. At the ora serrate, the diameter of the eye is 20 mm and the circumference is 63  mm; at the equator, the diameter is 24  mm and the circumference is 75  mm. Topographically, the ora serrata is relatively smooth temporally and serrated nasally. Retinal blood vessels end in loops before reaching the ora serrata. The ora serrata is in a watershed zone between the anterior and posterior vascular system, which may in part explain why peripheral retinal degeneration is relatively common. The peripheral retina in the region of the ora serrata is markedly attenuated. During intraocular surgery or trauma, dissociation of ora serrate can occur.

1.1.11 The Anterior Chamber Angle The anterior chamber is bordered anteriorly by the cornea and posteriorly by the iris diaphragm and the pupil (Fig. 1.9). The Schwalbe’s line, the periphery of Descemet’s membrane, forms the anterior margin of the sulcus; the scleral spur is its posterior landmark. Schwalbe’s line marks the termination of the corneal endothelium. The trabecular meshwork is triangular in cross section, with its base directed toward the ciliary body. It is composed of perforated sheets of collagen and elastic tissue, forming a filter with decreasing pore size as the canal of Schlemm is approached. The internal portion of the meshwork, facing the anterior chamber, is known as the uveal meshwork; the external portion, adjacent to the canal of Schlemm, is called the corneoscleral meshwork. The longitudinal fibers of the ciliary muscle insert into the trabecular meshwork. They are connected by elastic tissue to the trabecular meshwork. The scleral spur is an inward extension of the sclera between the ciliary body and Schlemm’s canal, to which the iris and ciliary body are attached. Efferent channels from Schlemm’s canal (about 30 collector channels and about 12 aqueous veins) communicate with the episcleral venous system.

1  General Anatomy

17 Epithelium Bowman’s membrane Stroma

Cornea

Descemat’s membrane

Trabecular meshwork

Endothelium

Canal of schlemm

Dilator muscle

Conjunctiva

Sphincter muscle

Scleral spur

Iris

Pigment layer Lens

Sclera

Zonular fibers Ciliary process Pars plana

Ciliary muscle Ciliary epithelium

Ora serrate

Fig. 1.9  Anterior chamber angle and surrounding structures. (Adapted from [2])

The depth of the anterior chamber varies. It is deeper in aphakia, pseudophakia, and myopia and shallower in hyperopia. In the normal adult emmetropic eye, the anterior chamber is approximately 3 mm deep at its center and reaches its narrowest point slightly central to the angle recess. The anterior chamber is filled with aqueous humor, which is produced by the ciliary epithelium in the posterior chamber. The fluid passes through the pupil aperture and drains chiefly by the conventional pathway through the trabecular meshwork into the Schlemm canal and partly by the nontrabecular uveoscleral drainage pathway, across the ciliary body into the supraciliary space. The uveoscleral pathway, thought to be influenced by age, accounts for up to 50% of aqueous outflow in young people. Contusion to the eyeball may lead to damage of the anterior angle and develop the increasing of the intraocular pressure. The relationship of the trabecular meshwork and the Schlemm canal to other structures is complex because the outflow apparatus is com-

posed of tissue derived from the cornea, sclera, iris, and ciliary body. The trabecular meshwork is a circular spongework of connective tissue lined by trabeculocytes. These cells have contractile properties, which may influence outflow resistance. They also have phagocytic properties. The trabecular meshwork can be divided into three layers: uveal portion, corneoscleral meshwork, and juxtacanalicular tissue, which is directly adjacent to the Schlemm canal. The uveal and corneoscleral meshwork can be divided by an imaginary line drawn from the Schwalbe’s line to the scleral spur. The uveal meshwork lies internal and the corneoscleral meshwork lies external to this line. The Schlemm canal is a circular tube closely resembling a lymphatic vessel. It is formed by a continuous monolayer of nonfenestrated endothelium and a thin connective tissue wall. The basement membrane of the endothelium is poorly defined. The lateral walls of the endothelial cells are joined by tight junctions. Larger vesicles (so-called giant vacuoles) have

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been observed along the internal canal wall. These vacuoles are lined by a single membrane, and their size and number are increased by increasing intraocular pressure. They are thought to contribute to the pressure-dependent outflow of aqueous. Approximately 25–30 collector channels arise from the Schlemm canal and drain into the deep and midscleral venous plexuses. Up to eight of these channels drain directly into the episcleral venous plexus as aqueous veins, which are visible in the conjunctiva by biomicroscopy.

1.1.12 The Lens The lens is a biconvex, avascular, colorless, and almost completely transparent structure, about 4 mm thick and 9 mm in diameter. It is suspended behind the iris by the zonule, which connects it with the ciliary body and is susceptible to the blunt contusion. Anterior to the lens is the aqueous; posterior to it, the vitreous. The lens capsule is a semipermeable membrane (slightly more permeable than a capillary wall) that will admit water and electrolytes. The lens contributes 20 D of the 60 D of focusing power of the average adult eye. The equatorial diameter is 6.5 mm at birth and increases in the first 2 to 3 decades of life, remaining in the region of 9–10 mm in diameter in late life. The anteroposterior width of the lens is about 3 mm at birth and increases after the second decade of life to about 6  mm at age 80 years. The lens consists of about 65% water, about 35% protein (the highest protein content of any tissue of the body), and a trace of minerals common to other body tissues. Potassium is more concentrated in the lens than in most tissues. Ascorbic acid and glutathione are present in both oxidized and reduced forms. There are no pain fibers, blood vessels, or nerves in the lens. After regression of the hyaloid vasculature during embryogenesis, the lens depends totally on the aqueous and vitreous for its nourishment. In youth, accommodation for near vision is achieved by ciliary muscle contraction, which moves the ciliary muscle mass forward and inward. This contraction relaxes zonular tension

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and allows the lens to assume a globular shape, causing a shortening of its anterior curvature. The increased lens thickness during accommodation is entirely due to a change in nuclear shape. With age, accommodative power is steadily lost. Adolescents have 12–16 D of accommodation, decreasing to 2 D at age of 50. Causes of this power loss include the increased size of the lens, altered mechanical relationships, and an increased stiffness of the lens nucleus secondary to changes in the crystalline proteins of the fiber cytoplasm. The lens epithelium lies beneath the anterior and equatorial capsule, but it is absent under the posterior capsule. Regional differences in the lens epithelium are important. The central zone represents a stable population of cells whose numbers slowly decline with age. An intermediate zone of smaller cells shows occasional mitoses. Peripherally, there are meridional rows of cuboidal pre-equatorial cells that form the germinative zone of the lens. Here, cells undergo mitotic division, elongate anteriorly and posteriorly, and form the differentiated fiber cells of the lens. In the human lens, cell division continues throughout life and is responsible for the continued growth of the lens. Germinative cells left behind after phacoemulsification can give rise to posterior capsular opacification as a result of aberrant proliferation and cell migration. In some open-globe injury cases, the spilled cortex from the capsule may cause foreign body reactive endophthalmitis. The lens has an outer cortex and an inner nucleus. The nucleus is the part of the fiber mass that is formed at birth, and the cortex forms as new fibers are added postnatally. In optical section with the slit lamp, lamellar zones of discontinuity are visible, differentiating the adult cortex into deep and superficial regions. In the fetal lens, this forms the anterior Y-shaped suture and the posterior inverted Y-shaped suture. As the lens ages, further branches are added to the sutures, each new set of branch points corresponding to the appearance of a fresh optical zone of discontinuity. The lens is held in place by a system of zonular fibers (Suspensory Ligaments) that originate from the basal laminae of the nonpigmented epi-

1  General Anatomy

Fig. 1.10  The case is a rupture, lens extruded (yellow arrow) after cutting the conjunctiva during one-stage repair surgery

thelium of the pars plana and pars plicata of the ciliary body. These fibers chiefly attach to the lens capsule anterior and posterior to the equator. Each zonular fiber is made up of multiple filaments of fibrillin that merge with the equatorial lens capsule. In Marfan syndrome, mutations in the fibrillin gene lead to weakening of the zonule and subluxation of the lens. The zonular fibers are susceptible to the trauma, especially with a contusion mechanism, and lead to the lens dislocation, subluxation, or extrusion (See Fig. 1.10).

1.1.13 The Aqueous Aqueous humor is produced by the ciliary body. Entering the posterior chamber, it passes through the pupil into the anterior chamber and then peripherally toward the anterior chamber angle.

1.1.14 Vitreous The vitreous is a clear, avascular, gelatinous body that comprises two-thirds of the volume and weight of the eye. The transparent vitreous humor is important to the metabolism of the intraocular tissues because it provides a route for metabolites used by the lens, ciliary body, and retina. Its volume is close to 4.0 mL. Although it has a gel-like

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structure, the vitreous is 99% water. The remaining 1% includes two components, collagen and hyaluronic acid, which give the vitreous a gel-­ like form and consistency because of their ability to bind large volumes of water. Its viscosity is approximately twice that of water, mainly due to the presence of the mucopolysaccharide hyaluronic acid. The vitreous adheres to the retina peripherally at the vitreous base, which extends from 2.0 mm anterior to the ora serrata to approximately 4.0  mm posterior to the ora serrata. Additional attachments exist at the disc margin, at the perimacular region, along the retinal vessels, and at the periphery of the posterior lens capsule. The base of the vitreous maintains a firm attachment throughout life to the pars plana epithelium and the retina immediately behind the ora serrata. The attachment to the lens capsule and the optic nerve head is firm in early life but soon disappears. The vitreous becomes more fluid with age and frequently separates from the inner retina (posterior vitreous detachment). The associated peripheral retinal traction is a potential cause of rhegmatogenous retinal detachment. Vitreous usually prolapse during surgery, especially when the posterior capsule is broken following phacoemulsification. In open-globe injured cases, vitreous can prolapse from the wound, which make the surgery more difficult.

1.1.15 The External Anatomic Landmarks Accurate localization of the position of internal structures with reference to the external surface of the globe is important in many surgical procedures. The transition zone between the peripheral cornea and the anterior sclera, known as the limbus, is defined differently by anatomists, pathologists, and clinicians. Although not a distinct anatomical structure, the limbus is important for two reasons: its relationship to the chamber angle and its use as a surgical landmark. The transition from opaque sclera to clear cornea occurs gradually over 1.0–1.5 mm and is difficult to define histologically. The corneo-

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scleral junction begins centrally in a plane connecting the end of Bowman’s layer and the Schwalbe’s line, the termination of Descemet’s membrane. The surgical limbus can be divided conceptually into two zones: an anterior bluish gray zone overlying clear cornea and extending from Bowman’s layer to the Schwalbe’s line and a posterior white zone overlying the trabecular meshwork and extending from the Schwalbe’s line to the scleral spur. Familiarity with these landmarks is essential to the surgeon performing a cataract extraction or a glaucoma-filtering procedure. The distance of structures from the limbus as measured externally is less than their actual length. In adults the ora serrata is about 6.5 mm behind Schwalbe’s line on the temporal side and 5.7  mm behind it nasally. Externally, the ora serrata is situated approximately 5.5  mm from the limbus on the medial side and 7 mm on the t­emporal side of the globe. This corresponds to the level of insertion of the rectus muscles. The safest posterior surgical approach to the vitreous cavity or injections into the vitreous cavity through the pars plana should be given 3.5–4.0 mm from the limbus in the phakic eye and 3–3.5 mm from the limbus in the pseudophakic or aphakic eye (Fig.  1.11). The pars

IR

O.S.

OD

Fig. 1.11  IR  =  intraocular irrigation (infratemporal, at the site of red dot), O.S.  =  ora serrate. Blue dotted line is the imaginary line of the ora serrate during vitreoretinal surgery

plicata, which is the target for cyclodestructive procedures in the treatment of intractable glaucoma, occupies the 2–3  mm directly posterior to the limbus. The foveal avascular zone (FAZ), or capillary-­ free zone, is an important clinical landmark in the treatment of subretinal neovascular membranes by laser photocoagulation. Its location is approximately the same as that of the foveola, and its appearance in fundus fluorescein angiograms varies greatly.

1.2

Anatomy of the Visual Pathway

Caiyun You

1.2.1 Retina • Periphery: 1000 photoreceptors per ganglion cell. • Macula: 1 photoreceptor per ganglion cell. • Similar arrangement in the cortex: number of cortical cells responding to foveal stimulus 1000× peripherally. • Papillomacular bundle: from macula horizontally to optic nerve. • Superior and inferior retina outside the macula. –– Fibers travel in an arc around the papillomacular bundle. –– Enter the optic nerve at superior and inferior poles. –– Damage can cause arcuate defects. • Nasal retina: fibers travel directly to optic nerve. • Field defects caused by retinal pathology from trauma: –– Field defects from retinal lesions do not respect the vertical meridian. –– Arcuate lesions will respect the horizontal meridian. –– Maculopathy may cause a central scotoma.

1  General Anatomy

1.2.2 Optic Nerve • 1.2 million retinal ganglion cell axons –– Run toward the disk in an arc in the temporal region of the retina, without crossing the horizontal raphe. –– Run straight toward the disk nasally. –– After entering the disk, the peripheral nerve fibers remain on the outside of the optic nerve, while the fibers representing the central parts of the visual field run in the center of the optic nerve (Fig. 1.12). • Four divisions: –– Intraocular 1 mm –– Intraorbit 25–30 mm

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–– Intracanalicular 4–9 mm Susceptible to injury because of tight compartment –– Intracranial 10 mm prior to chiasm • Blood supply: –– Prelamina: retinal arterioles –– Lamina: short posterior ciliary arteries –– Orbit: central retinal artery and pial arteries –– Intracanalicular: ophthalmic artery –– Intracranial: ophthalmic artery and carotid artery Blunt injuries to the eye can cause bleeding into the optic nerve sheath or tearing of the tiny pial blood vessels that supply

Retina

Optic nerve

Chiasm

Optic tract Lateral geniculate body

Optic radiation

Fig. 1.12  Anatomy of visual pathway

Occipital cortex

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the nerve, both resulting in complete, irreversible loss of vision on the affected side [1] • Sclera and choroidea are very thin at the site of penetration, and the sclera is perforated (lamina cribrosa) [5] –– Evulsion (see below) • Once the extremely delicate nerve fibers have passed the sclera, they become enveloped by myelin sheaths. –– Do not have Schwann cell sheaths –– As part of the brain, the optic nerve is surrounded by meninges –– The dural sheath and the arachnoid sheath merge with the sclera –– Between arachnoid sheath and pial sheath lies a cerebrospinal fluid-filled space which makes a shift between nerve and sheath possible [6]

1.2.3 Anterior Junction Syndrome • Corresponding to the new order of the nerve fibers, visual field defects oriented to the vertical midline are demonstrated from damage to the prechiasmatic region. • The nasal nerve fibers run in the same direction as the opposite optic nerve toward the opposite side before they reach the optic tract. • There are marked defects in the visual field in one eye, while a deficit in the temporal half of the visual field of the other eye may be only suggested. • Due to asymmetry in the involvement of the eyes, RAPD can often be observed with lesions in this area.

1.2.4 Chiasm • 8 mm long, 12 mm wide, 4 mm thick • 10 mm above the sella • It is limited on both sides by the carotids and cavernous sinus, by the hypophysis below, by the ethmoidal cells anteriorly, and by the floor of the third ventricle above.

–– Spatial narrowing and the high density of the visual information. –– Damage can lead to blindness in both eyes. • Axons in the optic nerve from the temporal retina do not cross • Axons in the optic nerve from the nasal retina do cross –– 53% of optic nerve axons are nasal • Pathology in the chiasm affects the crossing fibers. –– Axons from the nasal retinas affected and temporal field defects in both eyes (bitemporal defect), with lots of variability –– The RAPD is on the more severely affected side.

1.2.5 Optic Tract/Lateral Geniculate Nucleus (LGN) • From the chiasm, fibers precede posteriorly toward the lateral geniculate. –– Some fibers leave prior to the LGN. –– Left lateral geniculate receives: Fibers from the nasal retina of the right eye, right side of the world. Fibers from the temporal retina of the left eye. • Characterized by homonymous visual field defects on the side opposite to the lesion, which are limited by a vertical midline (Fig. 1.13). • Asymmetric: the more posterior the lesion in the optic pathway, the more symmetrical the homonymous defects become.

1.2.6 Optic Radiations • Pathways from the LGN to the cortex. –– Travel through parietal and temporal lobes. • The inferior parts of the visual field are supplied by the superior parietal neurons, the superior parts of the visual field by the inferior temporal neurons. • The far peripheral temporal crescent is represented anteriorly in Meyer’s loop, which

1  General Anatomy

23

Visual fields L

R 1 Retina Optic nerve 2

1 Optic chiasma 2

3

Optic tract

3

4

5

Lateral geniculate body 4 Optic radiation

Occipital cortex

Fig. 1.13  The visual pathway and defects in the visual fields. (Adapted from [1])

has no homonymous part in the opposite side. • Lesions here are located in the temporal lobe at the anterior horn of the lateral ventricle. • Posterior to chiasm, therefore both eyes.

1.2.7 Occipital Cortex • Area of V1/striate/Brodmann 17. –– 55% of cells in striate cortex respond to stimuli within the central 10 degrees –– 80% respond to central 30 degrees –– Divided by the calcarine fissure into an upper and a lower part. The lower visual field is represented above and the upper visual field below the calcarine fissure.

–– The more peripheral parts of the visual field are represented more anteriorly. –– The temporal crescent is represented furthest anteriorly. • Occipital lobe disease: –– May manifest as quadrantic homonymous hemianopsia. –– Macular sparing (if posterior pole of the occipital lobe is spared; usually has normal visual acuity). –– Monocular temporal crescent (if anterior pole is spared). –– Checkerboard field, ipsilateral facial pain (V1), or loss of high spatial frequency or contrast sensitivity. –– Vision may be blurred despite 20/20. –– Micropsia, macropsia, metamorphopsia, or unformed visual hallucinations [6].

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Special Concerns

• Occipitotemporal lesion, medial, bilateral: prosopagnosia (difficulty recognizing familiar faces). • Parietal, dominant lobe (visual association areas, Brodmann’s areas 18, 19): alexia without agraphia (reads but cannot write), visual agnosia (sees the image but without meaning), optic agnosia (cannot say name of identified object). • Gerstmann’s syndrome: left-right confusion, finger agnosia, dysgraphia, dyscalculia. • Parietal, nondominant lobe (visual association areas): prosopagnosia, visual hemifield agnosia, hemineglect. • Parietal, bilateral (visual association areas): cortical blindness, usually not simultaneous; pupil reflex is still present. Patients may also have achromatopsia, loss of stereopsis, and stepwise return of vision (motion perception returns first, then light perception, color, central vision, then last visual association). Riddoch’s phenomenon observed if patients are blind but able to perceive objects in motion. • Anton’s syndrome: patients deny being blind. • Balint’s syndrome: bilateral posterior parietal stroke causing psychic paralysis of gaze (ocular apraxia, unable to make voluntary eye movements but spontaneous movements intact), simultanagnosia (difficulty processing more than one thing), and optic ataxia (difficulty looking at more than one thing). • Temporal lobe disease: formed visual hallucinations.

1.3

Anatomy of the Ocular Adnexa

Ling Yuan

1.3.1 Orbit The structure of the orbit involves seven bones, which are the frontal bone (orbital roof), the zygomatic bone (lateral wall and floor), the maxilla bone (floor), the lacrimal bone, the ethmoid bone (medial wall), the palatine bone, and the sphenoid bone (blunt tip) [7]. They form the four-­edge subuliform osseous concave, which is a bottom edges forward and a tip backward, with approximately a depth of 4.0–4.5 cm and a volume range between 25 and 30 mL (Fig. 1.14). There is an eyeball, and some fat, muscles, nerves, vessels, fasciae, and lacrimal glands in the orbit. The orbit is adjacent to the frontal sinus, the ethmoid sinus, maxillary sinus, and sphenoid sinus. As a result, some inflammation or some tumors of the paranasal sinuses could extend to the orbit directly. There is an optic foramen, a superior orbital fissure, and an inferior orbital fissure in the tip of orbit. It is an optic nerve and an ophthalmic artery that is through the optic foramen. The superior orbital fissure, outside of the optic foramen, is passed by the oculomotor nerve, the trochlear nerve, the abducens nerve, the ophthalmic branch of the trigeminal nerve, and the vena ophthalmica. And, the inferior orbital fissure that is between the lateral and the inferior orbital wall is passed by the second branch of the trigeminal nerve and the infraorbital artery. There are the supraorbital nerve and artery via the supraorbital incisurae, which lies in the junction of one-third medial and twothirds lateral supraorbital margin (Table 1.1).

1.3.2 Palpebral Eyelid, playing a role in protecting the eyeball, is located in the front of the eye, covering on the surface of the eyeball. The roughly horizontal oval palpebral fissure is taken shape by the upper and lower palpebrae, the main structure of which is formed by a dense tarsus. The upper eyelid is bounded by the eyebrows, the margin of which lies

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Fig. 1.14  Anatomy of the orbit (Adapted from [1])

Levator palpebrae superioris

Superior rectus Optic nerve

Superior oblique Medial rectus Inferior rectus

Table 1.1  Seven orbital bones and its strength Strength Weakness

Bones Zygomatic, sphenoid, maxilla, frontal Palatine, lacrima, ethmoid

1–2 mm below the upper corneal limbus; the lower eyelid, the margin of which is at the level of the lower corneal limbus, continues to the facial region, bordering on the nasa-jugal crease. The connective area of skin and mucous membranes in the eyelid margin, between the anterior lip which grows 2-to-3-row eyelashes and the posterior lip which contains Meibomian gland orifices, is called the gray line. The holocrine Zeis glands and the apocrine Moll glands end in the hair follicles. The medial and lateral canthus are the junction of the upper and lower eyelid. The lacrimal caruncle is the small, pink, globular nodule at the inner corner of the eye. The structure of the eyelid tissue from outside to inside is divided into five layers, the skin, the subcutaneous tissue, the muscle, the tarsal, and the palpebral conjunctiva, as follows (Fig. 1.15) [7]: 1. The skin. It is thin, rich in small blood vessel, and easy to form wrinkles. 2. The subcutaneous tissue. It is a loose connective tissue, and contains a small amount of fat.

Levator muscle of muller

Levator expansion Orbicularis oculi

Opening of meibomian gland

Fig. 1.15  The eyelid (Adapted from [1])

Therefore, during inflammation or trauma, it is easy to edema and subcutaneous hemorrhage (Fig. 1.16). 3. The muscle. There are two main muscles. One is the orbicularis oculi muscle, of which the

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close to the back of the tarsus, and is unable to move, clearly having tiny blood vessels in it. At a 2-mm distance from the inner side of the upper eyelid margin, a shallow trench calls the inferior tarsus sulcus, paralleling to the eyelid. Some foreign bodies could be frequently found in it.

Fig. 1.16 Periocular-lid laceration: sharp object (saw) induced periocular-lid laceration and with intact globe injury in a young man; laceration of eyelid, intraorbital adipose tissue prolapse, and levator palpebral muscle rupture

muscle fibers almost parallel eyelid margin. Blinking and closing of the lids is performed mainly by this muscle which is innervated by the facial nerve. Another is the levator palpebrae muscle, originating from the annulus of Zinn in the orbital apex, along the superior orbital wall, forward fanning out to the orbital rim. A portion of aponeurosis of the levator palpebrae muscle stops at the upper edge of the eyelid, and other portions of aponeurosis link to the subcutaneous tissue of upper lid passing through the orbicularis oculi muscle. Those muscles, innervated by the oculomotor nerve, and superior and inferior tarsal muscles, innervated by the cervical sympathetic nerve, also open the lids. The sensory innervation of the upper and lower lid is through branches of the first division and the second division of the trigeminal nerve, respectively. 4. The tarsal. The tarsal plate, which is the bracket of the eyelids, is a dense cartilage-like connective tissue. There are two strip-like connective tissues at inside and outside ends of tarsus, namely internal and external canthus ligament. Meibomian glands arranged vertically in the tarsal plate, opening in the palpebral margin, excrete the sebaceous liquid, which forms the surface layer of the tear film. This sebaceous excretion plays an important role in the stability of the tear film and preventing from the water evaporation. 5. The palpebral conjunctiva. Palpebral conjunctiva, a transparent smooth mucous tissue, is

1.3.2.1 Blood Supply 1. Dual anastomoses of the lateral and medial palpebral arteries in each lid [8]. 2. Anastomoses with the facial arterial networks [8]. 3. Posterior conjunctival artery [8]. 4. The palpebral vein converges into ophthalmic veins, temporal veins, and facial veins, and these veins do not have the venous valve. Some suppurative inflammation, therefore, could spread to the cavernous sinus, causing intracranial infection. 1.3.2.2 Lymphatic Drainage [8] 1. The lateral two-thirds of the lids drain to the superficial parotid nodes. 2. The medial lids drain to the submandibular nodes.

1.3.3 Conjunctiva Conjunctiva is ocular structure which was injured frequently. If the damage is limited to the conjunctiva, surgical intervention is rarely required. One of the most important factors of conjunctival injury is that there may be more severe ocular trauma. Conjunctiva is a thin transparent mucous tissue, covering on surfaces of tarsi and the sclera. According to the anatomic site, it includes the palpebral, the bulbar, and the fornix conjunctiva [7]. These three-part conjunctivas and the cornea in front of the eye constitute a cystic space, the palpebral fissure forming the opening, which is called the conjunctival sac. The palpebral conjunctiva has been described above. The bulbar conjunctiva, which can be moved, covers the front part of the sclera, attaching loosely. Where transiting to the corneal epithelium in the limbus, the bulbar conjunctiva attaches tightly. The f­ ornix

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e­ nding in the lateral upper conjunctival fornix, secreting tears with a 24-h volume of approximately 10 mL. The tear fluid is low in protein and of low viscosity. The secretory parasympathetic innervation follows the facial nerve, and the sympathetic innervation is through the cervical sympathetic. Tears contain a small amount of lysozyme and immunoglobulin A.  Therefore, it has a bactericidal effect.

Fig. 1.17  Bulbar conjunctival congestion after eye injury

conjunctiva is a mutual transitional part between the palpebral conjunctiva and bulbar conjunctiva. It is so loose that eyeball can turn freely (Fig. 1.17). Secretion glands, such as conjunctival goblet cells and the accessory lacrimal gland, secrete some mucin and fluid excretion. It participates in the tear film, maintaining the protection function of the ocular surface.

1.3.4 Lacrimal Apparatus 1.3.4.1 Lacrimal Gland Injury of the lacrimal apparatus is a frequent occurrence in war or in peacetime. In order to recover the lacrimal drainage function, it is important to treat the wound timely after injury. Glands of basal tear secretion include the serous gland (consisting of Krause gland and Wolfring gland), the mucous gland (consisting of conjunctival goblet cells, Manz gland, and Henle gland), and the lipid gland (consisting of Meibomian gland, Zeis gland, and Moll gland). These glands are no innervation. However, these tears form a lacrimal film, providing the basic function of tears. With an emotional response or stimulating the eye, the main lacrimal gland will secrete a large number of tears, which is called reflection secretion. The main lacrimal gland, which is a tubuloalveolar gland, lies in the lateral superior border of the orbit. There are 6–12 excretory ducts

1.3.4.2 Lacrimal Passage The whole lacrimal passage consists of a bone lacrimal passage and a membranous lacrimal passage (Fig. 1.18) [7]. Bone Lacrimal Passage The bone lacrimal passage includes the fossa of lacrimal sac and the nasolacrimal duct. 1. The fossa of lacrimal sac. It is located at the inferior medial orbital wall. The front of fossa of lacrimal sac is the maxilla frontal process, and the back is the lacrimal bone. The prozone of the fossa is the crista lacrimalis anterior, which is an anatomic landmark searching for lacrimal sac. And the posterior boundary of the fossa is the crista lacrimalis posterior. The average length of the fossa is 14.25–17.86 mm, the width is 7.6–8  mm, and the depth is 2.62 mm. 2. The nasolacrimal duct. Nasolacrimal duct starts from the fossa of lacrimal sac, extending downward to the inferior nasal meatus. The lateral wall of it is the lacrimal sulcus of the maxillary process, and the medial wall, which is fragile, is constituted by the descending process of the lacrimal bone and the ascending process of inferior nasal concha. There is rich morphological diversity of the bone lacrimal passage. The average length is 10–12 mm, with the maximum value being 15 mm and the minimum value being 2.5 mm. Its anteroposterior diameter is slightly greater than the transverse diameter that is averagely 4.6 mm. Its outlet is about 16 mm apart from the front-­ end of the inferior nasal concha, and about 17  mm apart from the bottom of the nasal

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28 Fig. 1.18  The lacrimal passageway (Adapted from [1])

Upper punctum Sac

Canaliculus

Nasolacrimal duct

c­ avity. The top and middle part of the duct is slightly narrow. The duct inclines backward 15–20 degrees, and slightly tilts outward. Membranous Lacrimal Passage The tear disposal system of the eye consists of the punctum, the canaliculi, the lacrimal sac, and the nasolacrimal duct. 1. The punctum. Beginning of the drainage of tears is from the punctum, which lies in papillae of the upper and lower eyelid margins. Diameter of it is about 0.2–0.3 mm. The punctum is close to the lacrimal lake, which is in favor of draining tears. 2. The canaliculi. The canaliculus is an about-­ 10-­mm-length small tube, connecting between the punctum and the lacrimal sac. At the beginning of 2 mm at the end of the punctum, the canaliculus routes perpendicular to the eyelid margins. Before arriving at the lacrimal sac, the upper and lower canaliculus used to converge to be a common canaliculus. But in some people, the upper and lower canaliculus open individually into the lacrimal sac, respectively.

3. The lacrimal sac. Lacrimal sac is located in front of the lacrimal sac fossa at the inferior medial orbital wall. It is the most dilated portion of the lacrimal passage, below the medial canthus ligament. There is a blind end at the top, and a lower end at the bottom that connects with the nasolacrimal duct. The length is 12 mm, and the width ranges from 4 to 7 mm. 4. The nasolacrimal duct. The nasolacrimal duct is situated in the bones of the nasolacrimal duct. The upper end of the nasolacrimal duct connects with the lacrimal sac, and the lower opens in the inferior nasal meatus. The tears are spread across the eye by blinking, and flow down across the eye along the lid margins toward the lacrimal lake which is located in the inner canthus. Subsequently, the fluid passes from the upper and lower puncta mainly by capillarity into the lacrimal canaliculi, through the lacrimal sac, and down the nasolacrimal duct into the lower nasal passage. Under normal conditions, the quantity of tears secreted should equal the quantity eliminated. In case of blocking in any sites of the lacrimal passage, epiphora could occur.

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Fig. 1.19 The extraocular muscles (Adapted from [1])

Superior oblique

Superior rectus

Lateral rectus Inferior rectus Medial rectus

Optic nerve

Superior rectus

1.3.5 Extraocular Muscles Extraocular muscles control eye movements. There are six extraocular muscles per eye, namely, four recti and two oblique muscles. It is, respectively, the inferior rectus, the medial rectus, the superior rectus, the lateral rectus, the superior oblique, and the inferior oblique muscles (Fig. 1.19) [7]. All rectus muscles and the superior oblique muscle start from the annulus of Zinn in the orbital apex. In addition, the inferior oblique muscle begins from the inferior margin of the orbit. All of them attach to the sclera of eye near the equator. When a certain muscle contraction occurs, the eyeball can turn to a certain direction. The function of the medial rectus muscle is adversion; the lateral rectus is abversion; the superior rectus is mainly sursumversion, secondly, adversion and internal rotation; the inferior rectus is mainly deorsumversion, secondly, adversion and external rotation; the superior oblique is mainly internal rotation, secondly, deorsumversion and abversion; the inferior oblique is mainly external rotation, secondly,

sursumversion and abversion. It is the oculomotor nerve that dominates the inferior rectus, the medial rectus, the superior rectus, and the inferior oblique muscles. Moreover, the lateral rectus muscle is dominated by the abducens nerve, and the superior oblique by the trochlear nerve. But these muscles cannot move individually; there should be mutual cooperation and coordinative activities between the muscles. When there is a muscle paralysis, or the dominative neural paralysis, those muscles will lose coordination. So, the deviation of eye position can occur, and patients complain about a double vision chiefly.

References 1. Galloway NR, Amoaku WMK, Galloway PH, et  al. Common eye diseases and their management. 3rd ed. London: Springer; 2006. 2. Riordan-Eva P, Whitcher JP.  Vaughan & Asbury’s general ophthalmology, 17th Edition. http://www. accessmedicine.com 3. Jian Ge. Ophthalmology. People’s Medical Publishing House Co., LTD, 2005.

30 4. Feng K. Clinical research and prevention of blindness for serious mechanical eye injury. Peking University doctoral degree thesis, 2012. 5. Kahle W, Frotscher M.  Color atlas ad textbook of human anatomy, vol. 3. New  York: Thieme; 2003.

K. Feng et al. 6. Goodman RL.  Ophtho notes: the essential guide. New York: Thieme; 2003. 7. Lang GK, Amann J. Ophthalmology: a short textbook. Stuttgart: Thieme; 2000. 8. Timothy LJ.  Moorfields manual of ophthalmology, Vol. 1–2. 2014.

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Ocular Structure Change and Specific Feature When Encountered with Trauma and Pearls Hua Yan, Caiyun You, and Ling Yuan

Abstract

The eyeball has its specific anatomic changes besides the general anatomy when facing an ocular condition. This chapter aimed to discusses the ocular structure change when encountered with trauma, and how specific feature of a structure make it more likely to be injured. Keywords

Eyeball · Traumatic optic neuropathy Precanalicular injury · Canalicular injury The orbital trauma · Motor nerves of the orbit smooth muscles

2.1

Eyeball

Eye globe is a complex structure of sensory organ. It is susceptible to trauma, although there is protection of orbit. Serious mechanical eye injuries are not uncommon. The cornea is the fine H. Yan (*) · C. You Department of Ophthalmology, Tianjin Medical University General Hospital, Tianjin, China e-mail: [email protected] L. Yuan Department of Ophthalmology, First Affiliated Hospital of Kunming Medical University, Yunnan, China e-mail: [email protected]

tissue that is exposed to the outside, so it is ­susceptible to trauma and difficult to recover its optical properties after injury. In the case of severe ocular trauma with vitreous hemorrhage, high intraocular pressure easily leads to corneal blood stained, which can make the intraocular exploration more difficult. The lens and the iris are prone to extrusion while severe mechanical ocular trauma occurs, especially in the case of eyeball rupture. Due to the special position of the ciliary body and the unique role in maintaining the shape of the eyeball, the degree of ciliary body injury is key to the future fate of the eyeball. The ciliary body is easy to detach under the external force. The ciliary process atrophy and formation of ciliary membrane occur a period after eye injury. All of the ciliary body damage can lead to the eyeball atrophy. Retina is the main affected tissue in the eye injuries involved with sclera. Retinal damage can cause the release and proliferation of RPE cells and lead to traumatic PVR, which directly resulted in retinal traction and detachment. Almost all the vitreous prolapse in openglobe injured eyes is due to a sudden drop of IOP.  The vitreous will prolapse and drag the whole retina into the wound tract and then a closed funnel is formed. It is even more difficult for clinicians to deal with the closed-funnel retinal detachment caused by severe ocular trauma that is also a major risk factor for poor prognosis of injured eyes.

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Choroidal tissue rupture can easily occur under the external force. Besides, when severe eye globe rupture occurs, sudden drop in intraocular pressure can cause an outbreak of massive suprachoroidal hemorrhage, which can make the ocular tissue extruded out of the eyeball due to high pressure and cause extremely serious consequences to the eye globe.

2.2

Visual Pathway

Eye injury may be present in the polytraumatized patients. The eye and the brain have many common anatomical and physiological properties, including being protected by bony walls, having firm fibrous coverings, and having a dual blood supply.

Pearls

• The defect in one eye only: It is anterior to the chiasm, or there is bilateral intraocular or optic nerve disease. • Any lesion post to chiasm: Both eyes. • The more posterior in the pathway, the closer together the fibers are. • More posterior lesions will cause more similar looking lesions in the two eyes. • More anterior lesions: Less similar.

• Optic disc swelling/papilledema: –– Increased intracranial pressure. Such as subdural hematoma. –– Compression/ischemia, etc. –– Relative afferent pupillary defect (RAPD) on affected side.

2.2.2 Precanalicular Injury • Because of its redundant course in the orbit, the intraorbital optic nerve is only rarely injured by trauma, as it is mobile to some extent. • Injuries can occur especially due to direct injury (e.g., foreign body). • If the optic nerve is injured within 1 cm behind the globe, central retinal artery occlusion may also be seen. • If the injury lies further posteriorly, no changes are seen in the fundus. Vision can deteriorate further after the injury due to compression on the optic nerve sheath as a result of a hematoma. • Evulsion: In worst case, the nerve can be avulsed from the globe; evulsion may be aided by increased intraocular pressure (IOP) that “pushes” optic nerve out of scleral canal (Fig.  2.1a) or increased intraorbital pressure that pushes globe anteriorly, stretching the nerve (Fig. 2.1b).

2.2.3 Canalicular Injury 2.2.1 Traumatic Optic Neuropathy • The optic nerve is involved in 0.5–5% of closed head injuries. • Shearing forces, often after blow to brow/ head. • Similar to spinal cord injury. • Mass trauma/hematoma may compress the optic nerve. • Altitudinal defect/central/centrocecal scotoma.

• In closed head injuries, often found following blows to the head, injuries of the optic nerve are usually canalicular. • The fracture of the optic canal is common, while resulting injury of the optic nerve by bone fragments is rare. • Presumably ischemic damage after compression or shearing of the vessels supplying the optic nerve. –– Intracranial injury.

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Fig. 2.1  Theories of evulsion

IOP

a b

• Axonal shearing of the intracranial part of the optic nerve can occur with a sudden movement of the brain with severe blows to the head. • Often with a RAPD with an unremarkable fundus.

Hints on Visual Defects in Traumatic Patients

• Retrochiasmal lesions (disorders of visual pathway posterior to the optic chiasm, i.e., from the optic tract to the visual cortex, injuries such as a contrecoup injury to the occipital lobe) cause homonymous visual field defects. • Generalized depression: Cataract/ other media opacity/refractive problem. • Big blind spot: Disc edema/optic nerve abnormality. • Arcuate/altitudinal: Branch retinal artery occlusion/ischemic optic neuropathy/other optic neuropathies. • Central/centrocecal: Maculopathy/all optic neuropathies. • Bitemporal: Parasellar.

2.3

Ocular Adnexa

2.3.1 The Orbital Trauma The orbital trauma is caused commonly by a blunt injury, a traffic accident, falling from a great height, etc. It could lead to an orbital fracture because orbital bone wall is thin, an intraorbital hemorrhage, and/or an optic nerve contusion. Due to the complexity of orbital structure and the importance of visual function, orbital blowout fractures have been the focus of interdisciplinary research. In maxillofacial injuries, orbital fractures of medial and posterolateral walls were most common, which often showed multiple wall fractures. In the case of the optical canal fractures, the end of fracture usually would oppress or damage the optic nerve so that the reaction of pupil to light could disappear or be slow. That is to say, under the ophthalmic exam, mydriasis could be found in those patients. In view of those huge forces in such damage, the patient should be examined systematically and comprehensively to make sure whether the systemic injury or the nervous system disorder exists.

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2.3.2 Medial Orbital Wall The medial walls of the orbits are approximately parallel to each other and to the midsagittal plane. The medial wall is composed largely of the thin lamina papyracea of the ethmoid bone. This plate is exceptionally fragile, measuring only 0.2– 0.4 mm in thickness. The lamina papyracea provides little resistance to expanding ethmoid sinus mucoceles and commonly transmits inflammatory and infectious processes from sinusitis into the orbit. The body of the sphenoid bone completes the medial wall to the apex posterior to the ethmoid bone. The medial wall ends at the optic foramen, where the sphenoid forms the medial wall of the optic canal. The anterior and posterior ethmoidal foramina are two openings within the frontoethmoid suture line in the superomedial orbit. The former usually lies 20–25 mm posterior to the anterior lacrimal crest, and the latter about 32–35 mm behind the anterior crest and 5–10 mm before the optic canal. The foramina transmit branches of the ophthalmic artery and nasociliary nerve into the ethmoid sinus and nose. These vessels frequently are injured in orbital trauma and are the major sources of subperiosteal hematomas. These openings are almost the level of the roof of the ethmoid labyrinth and the floor of the anterior cranial fossa. The cribriform plate may lie up to 10 mm below this level and medial to the root of the middle turbinate, which can be fractured during orbital or intracranial surgeries.

2.3.3 Orbital Septal System Suspended from the periorbita to form a complex radial and circumferential web of interconnecting slings are connective tissue septa. These septa form fine capsules around fat lobules and also surround the extraocular muscles, optic nerve, and neurovascular elements. The fascial slings provide support and maintain constant spatial relationships between these structures during ocular movements. These septa are responsible for the transmission of restrictive forces from

incarcerated extraocular muscles after trauma, even in the absence of true muscle entrapment. Septa that encircle the optic nerve may confine hemorrhage or air, which may result in compressive optic neuropathy after trauma.

2.3.4 Motor Nerves of the Orbit The extraocular muscles are innervated by the third, fourth, and sixth cranial nerves. The oculomotor nerve, being cranial nerve III, enters the orbit via two branches. The superior branch dominates the superior rectus and levator muscles. The inferior branch controls the inferior rectus, medial rectus, and inferior oblique muscles. With the inferior division of the oculomotor nerve run parasympathetic fibers that arise from the Edinger-Westphal subnucleus. These synapse in the ciliary ganglion lies lateral and inferior to the optic nerve at 1.5–2 cm behind the globe. They progress through the short ciliary nerves to the ciliary body and iris sphincter. Little redundancy occurs to these nerves, so they may be injured easily during orbital dissection. This results in disturbances of pupillary function and accommodation. The trochlear nerve (cranial nerve IV) passes through the extraconal space of the superior orbit to the superior orbital fissure above the annulus of Zinn. Then it crosses over the superior rectus and levator muscle complex. Before penetrating its substance in the posterior third of the orbit, it moves along the external surface of the superior oblique muscle. In this position against the orbital roof, the trochlear nerve is damaged easily during blunt trauma.

2.3.5 Smooth Muscles Smooth muscles are present in both the upper and lower eyelids and serve as accessory retractors which are controlled by the sympathetic nervous system. The supratarsal muscle of Müller in the upper eyelid originates from the undersurface of the levator muscle just anterior to Whitnall’s ligament. Then it moves downward, passing through

2  Ocular Structure Change and Specific Feature When Encountered with Trauma and Pearls

the posterior of the levator aponeurosis to which it is adherent, and finally inserts onto the anterior edge of the superior tarsal border. The sympathetic muscle is not quite clearly defined in the lower eyelid. Fibers go through posterior to the capsulopalpebral fascia and then insert 2–5 mm

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inferiorly to the tarsus. Horner’s syndrome is a result of disruption of sympathetic innervation to these muscles, which is characterized by ptosis, miosis, and ipsilateral anhidrosis of the face. Various clinical findings depend on the location of the lesion along the polysynaptic pathway.

Part II Examinations

3

Visual Function Examination Yun Feng and Baoqun Yao

Abstract

Vision is mainly limited to the optics of the eye through the anatomy and physiology of the visual system. In this way, vision acuity may be a key clinical measure to show the integrity of visual pathway optical and physiological states of the eyes. Each patient must first have a routine examination of the vision acuity, regardless of the initial visit or follow-­up visit. The central vision is the main sign of visual function, especially the far sight, which needs more attention. Whenever possible to use standard visual acuity chart (Snellen, ETDRS): A set of letter is set up, each letter as an integrity which is five times as large as each stroke; for patients who cannot read should use the none text chart (such as E, Landolt C) which is based on the same principles of the Snellen chart; for kindergarten children, use Allen cards, HOTV letters, or E games; for babies, use color objects, toys, or flashlights to determine vision by fixing or following objects.

3.1

3.1.1 Distant Vision 3.1.1.1 How Is the Visual Acuity Chart Designed? The size of the visual angle directly affects the stimulated area of the retina. The greater the angle of view is, the greater the area of stimulation of the retina. The distance of an object from the eye and the size of objects directly influence the angle of view. The farther away the object is, the smaller the angle of view; and the smaller the object, the smaller the angle of view. According to the astronomer, the angle between the two stars which can be judged separated from each other by the eye must be no less than 1 point (1/60 degrees). How big is 1 point of view, equivalent to the retina?

Keywords

Visual function examination · Vision acuity · Distant vision · Near vision

Y. Feng (*) Department of Ophthalmology, Peking University Third Hospital, Beijing, China B. Yao Department of Ophthalmology, Tianjin Medical University General Hospital, Tianjin, China

Visual Acuity

17,055 × 2π / 360 × 60′ = 4.96 µm.

The 1 point of view is about 4.96 μm on the retina. The diameter of cones ranged from 4.4 to 4.6 μm by Koster. So the 1 point of view is equivalent to 1 cone cell. To distinguish between two points, the excited two cones must be separated from at least one of the less excited cones. If the two excited cones are connected, they cannot be distinguished from each other by seeing them as a point. That is why a point of view is defined as the minimum angle of view for distinguishing two points?

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An eye chart is designed on the basis of this principle. Each letter consists of 25 small squares, each of which is equal to the design’s 1 point of view. The width and space of the strokes are 1 point of view. For the first line, the standard inspection distance is 5  m, that is, the width of each stroke of this row of letters, forming a 1 point of view at 5 m distance. Landolt C test has been recommended by some scholars and is used as the standard test when compared with other visual tests. The Landolt C is a broken circle. The width of the rest and the width of strokes are equal to a height of five. One of the four rings is displayed. There are several advantages to test Landolt C, including equal difficulty of all the targets (unlike the different letters in difficulty), sensitivity of astigmatism refractive error, and suitability for illiterate use. However, the Landolt C test is not widely used because it has a guess rate of 25%; so, an alternative is the specification of another visual target by comparing with its visual acuity the Landolt C test acuity. The principle of designing C rings (Landolt rings) is the same as Snellen chart, but the E is easier to identify than the C. The visual acuity chart of E was used to detect 1.0 eye, and only about 0.9 was checked with the C word visual chart. In the United States with the clinical chart, 0.1 by E, the remaining few lines are the standard for all English letters, so patients can read from left to right, for example: EGNU5 and FZBD4. The design of the near vision table is the same, but the examiner will change the distance to 30 cm. The Sloan letters, a set of 10 capitalized letters, is the most popular substitute. Visual acuity chart is designed based on the Sloan letters developed for the early treatment of diabetic retinopathy (ETDRS). The original ETDRS table has been replaced by 2000 instead of series. The revised ETDRS table is more accurately equivalent, which is widely used in currently clinical research.

3.1.1.2 Determination of Distant Vision For the patients with very poor vision, a clinician can use a finger count or hand move. This strategy is recommended by low eyesight, especially in trauma patients at emergency. If the patient is

Y. Feng and B. Yao

seated at 5  m from the visual chart, he can see only the line above the standard visual angle at the distance of 10 m, and the visual acuity is 0.5. This is an international way of recording, and it is the fractional representation of Snellen into decimal. In the Snellen recording, the numerator indicates the distance between the patient and the visual chart, which is the denominator required for the standard visual angle. Therefore, the visual acuity of the preceding example should be 5/10 (m per unit) (in the United States it is still measured in feet and the standard distance is 20 ft, so the record is 20/40). It can give a fairly good estimate of the patient’s vision in such a measurement, although not very accurate, but is sufficient for clinical practice. Distance itself does not have any effect on visual acuity, provided that the subject’s accommodative state and pupil size are controlled. It is rarely that the patient can see a single line of all symbols, but could not recognize one in the next line. The number of symbols on an eye chart is not arbitrarily chosen because the number of symbols is related to the visual representation of the symbol. In general, at least 2/3 symbols are required to be recognized to represent the vision acuity by the line symbol. For example, the line of 1.0, there are 8 symbols in this line. If you can only identify 2~3 symbols, you can’t have 1.0 vision, but only 0.9+2 or 0.9+3 vision. If only one or two can’t recognize it, the visual acuity is 1.0−1 or 1.0−2. If the first line of letters is not recognized, the patient is progressively moved closer to the eye chart until he can begin to recognize the big letter. If the first large letter is seen from the visual chart at 4 m, the visual acuity is 0.08 (4/50); the same principle is 0.06 at 3 m, 0.04 at 2 m, and 0.02 at 1 m. General hospitals are using mirrors, flat mirrors placed in front of the visual acuity 2.5 m. According to the principle of reflection from a plane mirror, see the patient in front of the mirror image in the mirror after the visual acuity at 2.5 m.

3.1.1.3 Things that Should Be Paid Attention To Certain things should be of concern before the test, such as the following: the tip of the stick that

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points to the vision chart should not be too fine; the diameter must be at least 2~3 cm and painted black; a plate after examination of an acute infectious keratoconjunctivitis patient must be disinfected; ametropia patients are used to squinting; the vision acuity is not the real vision while squinting; the testing time allowed for each marker shall not exceed 2~3  s; conjunctival secretion or tear may blur the vision. Visual acuity chart and the patient must be exactly 5  m apart; for the sake of convenience, visual acuity at 2.5  m before a mirror, but the visual chart to mirror, mirror to the patient, and the two distances should be 5  m. The mirror should be made of good quality, and the distorted mirror cannot be used. When the test is performed, the chart must be adequately illuminated and of high contrast. The vision chart must have standard illumination, and the illuminance should be about the same everywhere. How much is the standard of illumination? There are different versions: British Duke-Elder, Smith (1962), 100 foot candle; The United States Doesshate (1955) 200 lx, Emilenko (1956) 700 lx; Yitian, Japan (1938) 100  lx, Big Island (1950) 500 lx; Zhao Jinjia (1959) 100~200 lx, Sun yat sen Medical School (1964) 500~1000  lx; and also 100  cd/m2 in the Unites States to 300  cd/m2 in Germany. Both sides of the vision chart are equipped with a 20 W white fluorescent lamp, which is the best illumination. Take the two fluorescent lamps as close as possible, and adjust the height of the light from the height of the visual chart for 800~1300 lx. According to the physiology, vision decreases at dark light, while improves at bright illumination. According to the clinical experience, 1000 lx is the most suitable. lx is also known as lux, and is the same unit of illuminance foot candle. One foot candle = 10.764 lx, 1 lx = 0.0929 foot candle. Various types of visual dysfunction can change the effects of luminance on acuity. Visual acuity below 0.02: when the patient-­ faced visual acuity is 1 m and still cannot identify the vision chart. The patient sits in the backlight and fingers by 1 m far gradually move to the eye, until the patient begins to identify the number of fingers, then recording distance, the vision is * * cm refers to the number of fingers, for example,

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20 cm fingers counting and 40 cm fingers ­counting. Number index can be abbreviated as CF (counting fingers). The number of digits that cannot be identified at hand can be checked by hand movement. The physician moves the hand (the patient’s back to the sun) from the distance until it starts to recognize the hand. Manual entry also requires recording distances, such as 20 cm hand move, 40 cm hand move. Manually, it can be abbreviated as HM (hand movement). Patients with poor vision as finger counting or hand motion should be examined for light perception and light localization. In a dark room, a doctor holds a candle (or an equivalent brightness of light) at 5 m to test whether the patient can tell whether the candle is light or not. If there is 5 m identification of light, 5 m LP; if the lights cannot be seen at 5 m, then move closer to the 4 m, or even move closer to the front of the 1 m check, the visual acuity were 4  m light… 1  m light perception (light perception can be abbreviated as LP). People who are unable to recognize light perception can begin to record “no light perception” (abbreviated as NLP) and generally do not refer to distant vision as “blind” or “0”. With or no light perception does not seem to vary little, but they are extremely important for operation indications and prognosis. The light localization is testing light field of view. Let the patient point out the direction of the light with his finger. Lights should be placed in the right upper, right, right lower, lower, left lower, left, left upper, upper 8 directions in front of the eye less than 1 m, but cannot move in order, in case the patient guesses. You can use “+” to represent the direction accurately. “−” means the patient cannot identify the direction or identify the wrong direction.

3.1.2 Near Vision The principle of near vision is similar to far visual acuity, “according to the provisions of the standard chart,” check the eyes vision distance is 30 cm. Far and near vision recording method: far/ near. For example, 0.1/1.5  means distant vision of 0.1 and near vision of 1.5. Another example:

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/0.9 means near vision is 0.9. However, we do not comply with this rule and allow the subject to move appropriately to the limit of the best view. Near vision was 1.5, 1.2, and 1.0, respectively. If 0.1 cannot be seen notes “0”. If the sight distance is too near, it should be indicated, such as 1.5 (15  cm). However recent work shows that it is text spacing not letter size that limits reading speed. When the text spacing is closer than a critical spacing, reading is slowed, which means that space matters in near reading. Different countries have different methods of recording near vision. Some use fractional notation to indicate distant vision, such as 20/20, 20/100, etc. 20/20  =  1.0, 20/100 = 0.2. For near vision records, J.1 is normal near sight, J.7 is already near vision loss.

3.2

Visual Field

3.2.1 General Concept 3.2.1.1 Unit and Standardization Field of vision, like vision, is actually used to test the human eye’s perception of light, which belongs to a psychophysical examination. Compared with the central visual acuity test, field of vision tests the peripheral vision (Fig.  3.1). The electromagnetic wavelength that the human eye can detect is between 390 and 770  nm, called visible light. Colors that human eyes sense change according to different wavelengths. Normal eyes are most sensitive to the green light at 555 nm wavelengths. Although in physics the electromagnetic wave radiation energy unit Watt (Watts) is used as light units, in the field of view detection, the human eyes’ sense-related efficiency of light of different wavelengths needs to be considered, which is combined as the luminous flux. Therefore, in the actual visual field detection and literatures, an ancient unit of luminous flux—apostilb, ASB is used as the light unit. The background brightness of the perimeter may vary between 0 ~ 1000 asb. At the same time, perimeter detects eyes’ sensitivity to light to measure the visual function, in which light sensitivity is the smallest visible brightness and this brightness can be represented by the strength of the shown cursor. Currently, the Goldmann perimeter cursor is used as the

standard, taking its 1/10 log units as light sensitivity units, namely dB, decibel. For example, 10,000asb is equivalent to the Goldmann 4e filter, with a logarithmic unit of 0.0, indicating that the most powerful stimulus produced by the perimeter can detect eyes while eyes cannot perceive this brightness, so the light sensitivity is 0  dB; 100asb is equivalent to 2e filter, with a logarithmic unit of 1, or 10 dB; the weakest stimulus that an automatic perimeter can produce is 0.08 asb, corresponding to light sensitivity of 51 dB, and human eyes cannot reach this ideal value. Of course, even if the standard background light and cursor brightness are used, different pupil sizes, different eccentric directions of the light beam entering, and the opacity of the dioptric media all affect the brightness of the images on the retina. Therefore, except standardizations of operations and the statistic software, the background brightness and the colors and brightness of the cursor are the most vital parts of the current computer automatic perimeter so as to have comparability in analysis.

3.2.1.2 Difference Light Threshold What is the minimum visible brightness of the retinal light sensitivity in the field of vision? It can be understood by differential light threshold. In a constant background illumination, the visibility of stimulating cursor is 50%, which means that when cursors at different simulating strengths are shown in a site of the visual field repeatedly, dark cursors are always invisible (visible rate 0), while the light cursor is always visible (visible rate 100%), and if the perceived opportunity of a cursor at a certain strength is 50%, then the cursor’s stimulating strength is the difference light threshold of this check points. It is a threshold concept, or a doorsill problem in fact. When the ability reaches to or even exceeds this threshold or doorsill, then you can cross, and you can perceive the presence of light. So the difference light threshold is in inverse proportion to light sensitivity threshold. The higher the threshold is, the strength that the cursor needs is higher, and then the feeling of light is weaker, which means that the light sensitivity is lower, vice versa. When the No. 3 white cursor is used in the standard detection procedure, normal young people can see the

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Fig. 3.1  Visual field test

weakest stimulus in the center of the point of fixation, namely the greatest sensitivity (slightly below 40 dB). The normal sensitivity of the central 30 degrees of vision ranges from 20 to

40 dB. Visual defects’ sensitivity will be greatly decreased. The absolute defect in the visual field where the brightest cursor cannot be recognized is called “blind spot.”

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3.2.1.3 The Fluctuation of Light Threshold Visual field is a psychophysical examination with many interfering factors that the results of the visual field or even the specific site of the same patient changes. So, whether this change is the damage or improvement from the real visual field or the interference caused by other factors needs to be judged. In a visual field test (usually within 20 min), if the result of multiple light threshold measurements on the same spot is discrete, it is called short-term fluctuation, SF.  The average SF of a normal person is between 1 and 2 dB. In diseases such as glaucoma, before the emergence of a specific dark spot, the first performance of this part is the increases of the discrete light threshold, namely the increases of SF.  The main factors affecting SF include the measures in light threshold tests, the sensitivity of the retina, the cooperation of the tested person, and false positive and false negative reaction rate, etc. SF is the basis for the evaluation of partial visual field defects, that is, any partial light sensitivity needs to be reduced to higher than SF to be meaningful. For the visual tests in different times, due to the physiological reaction state of the visual system have certain differences, coupled with the impact of learning effect, the subjects’ mental state and the IOP fluctuation, the light threshold measured in ­different times is also different. The inconsistence of the results in two tests is known as long-term fluctuation, LF. For normal subjects, the homogeneous LF is between 1 and 1.2 dB, and the inhomogeneous LF is between 0.8 and 1.3 dB. LF is the premise of quantitative visual field review and comparison. Only if the LF is within normal range can the visual field follow-up evaluation be done.

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The Absolute Boundary of the Visual Field Reaches a Certain Range The normal range of vision is greater than 90 degrees of the temporal side, 60 degrees of the nasal side, 60 degrees of the upper part, and 70 degrees of the lower part. The visual field of the left and right eyes can be superimposed on the nasal side so that the binocular visual field reaches 210 degrees on the horizontal range, 130 degrees on the vertical range, and about 30 degrees between the temporal peripheral eyes not overlapped. The most effective range of visual field is in monocular central 30 degree, which can provide clear visual image and color information, and it is also the focus of modern visual evaluation. The Light Sensitivity Is Normal in Every Spot of the Full Visual Field Except physiological blind spots, there should not be regions of scotoma where light sensitivity falls. The sensitivity of normal visual field reaches the highest level in central gaze, and gradually decreases with the increase of eccentricity.

3.2.2.2 Island of Vision The above words described a three-dimensional island shape, which not only covers an area, but also have different areas of different altitudes, which is described by Traquair as island of vision. The island area represents the visual range, and the altitude represents the sensitivity. Each point on the retina has a corresponding position on the island of vision, and the center of the eye corresponds to the fovea, which has the highest photosensitivity, that is, the peak of the island; the peripheral visual field corresponding to the peripheral retina has comparatively lower sensitivity, which constitutes the lower part of the island of vision. 3.2.2 General Knowledge of Visual Field Since the nerve fibers of the temporal retina are more concentrated, the corresponding nose side island of vision is relatively sharp with the 3.2.2.1 The Concept of Normal Visual Field increases of the eccentricity and the decrease of The normal visual field includes the aforemen- altitude, while the altitude of the temporal side tioned range and degree, which is a three-­ island of vision is gentler. The physiological blind spot is a vertical deep hole formed on the dimensional concept:

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temporal side of the island of vision. A vertical cutaway on any point of the island of vision can get a two-dimensional section. The vertical axis of the island represents the light sensitivity of each point. Each point on the horizontal axis represents different eccentricities on the longitude.

3.2.2.3 Isopter The vertical elevation at any point on the island of vision is the light sensitivity of the point. The attachment between points at the same vertical height is the attachment between each point of the same sensitivity, called the contour line of the island of vision, namely isopter academically. On the island of vision, different light sensitivity can map several isopter circles with different sizes. As mentioned earlier, different parts of eccentricity have different isopter circles distance. On a normal island of vision, the central part has comparatively smooth slope and large isopter distance; however, on the surrounding parts of the island of vision, especially around the nasal side, the slope is steep and the isopter distance is more crowded. Dynamic visual field test is conducting an isopter draw of different cursors, while the graphic pages in the results of the static visual field test shows the outline of the island of vision. 3.2.2.4 Physiological Blind Spot The optic disc itself has no photoreceptor cells, no photoreceptor function, so there is an absolute scotoma in the corresponding temporal field side of central area, namely the physiological blind spot. Its location and range are relatively constant, at 15.5 degrees temporal from the center fixation point, 1.5 degrees below the horizontal line, and with an area of about 6~8 degrees. The optic disc corresponds to the absolute scotoma, which cannot perceive cursors at any kind of stimulus strength. Meanwhile, the relative scotoma surrounds absolute scotoma and corresponds to the retina around the optic disc, which has low retinal sensitivity and can perceive improved strength of cursors. Some eye diseases can be manifested as enlarged physiological blind spots.

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3.2.2.5 The Symmetry of the Normal Field of Vision The eyes of normal people are approximately equal in size, the shape is basically the same, and the average light sensitivity of central visual field is basically symmetrical. Take the central fixation point as the center, the horizontal and vertical axes of vision will be divided into four quadrants, with macula central fovea as the boundary, the nasal, temporal, up, and down retinas, respectively, correspond to central fixation point bounded temporal, nasal, down, and up visual field, which takes central fixation as the boundary. Clinically, a range within 30 degrees is known as the central visual field. Since most of the RGCs distribute in this area, the central visual field is the most commonly used vision detection range, and the area between 5 and 25 degrees is traditionally known as the center area or Bjerrum area, where lies an important part of glaucomatous visual field detection. The area outside 30 degrees is called peripheral visual field.

3.2.3 Clinical Perimetry and Perimeter Categories Clinically, we usually perform monocular vision tests on both eyes for binocular contrast, and sometimes binocular tests such as assessing the visual field of the driver are also conducted. No matter what kind of examinations, we should stress the problem of checking the fixation of the eye. In a fixed state, a cursor, being displayed on an evenly lighted background, is dynamically or statically shown to test the difference in light threshold or visibility range.

3.2.3.1 Kinetic Test In the field of vision, the intensity of the weakest spike laser target that is exactly visible at each point, i.e., the light sensitivity level of the point, is referred to as the optical threshold. The attachment of the adjacent points at the same threshold or the light sensitivity is the isopter of the stimulus cursor at that strength. Outside of the isopter, the cursor cannot be seen (which belongs to subthreshold stimulus). When it is just visible (threshold) and

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belongs to suprathreshold stimulus, then the cursors at each spot within this range should be seen. Therefore, isopter is the boundary that separates the area where the cursors can be seen or not. Kinetic test means that the cursor at certain strength is moved from surrounding invisible area to the visible area so as to detect the spot that can just be seen, and to surpass twice, depicting isopter at this strength and other strength level. In the visual field image, it is shown by the isopter image with cursors at different stimulus strengths. Kinetic test can quickly and easily detect the narrowed or depressed visual field, but it is easy to ignore the small and deep defects in the field of vision, and is often used for screening the damage of the visual system. The normal monocular vision range, due to the impact of the eyes, eyelids, and nose, is 60 degrees on the upper side, 75 degrees on the downward side, the nasal side is 60 degrees, and 100 degrees on the temporal side. The center of physiological scotoma is 15.5 degrees from the temporal side, 1.5 degrees below the horizontal line, 8 degrees of the vertical diameter, and 6 degrees of the horizontal diameter. In accordance with the contour of the island of vision, the isopter circle is in a slightly horizontal oval shape, and the distance between different lines of sight is relatively larger at the temporal side and relatively crowded on the nasal side.

3.2.3.2 Static Test At a certain point in the field of view, a cursor with a range of different stimulus intensities is presented, and the intensity of the 50% visible cursor stimulus is the threshold (dB) of this point, which is used to determine the degree of photosensitivity of different visual points within the field of vision. In a static test, an estimated visible threshold stimulus is presented firstly, and when the reaction cursor was seen, the cursor stimulus intensity decrease in a 4 dB speed until the eyes cannot see, then increase in a 2 dB speed until the checked eye can see, so the sensitivity or light threshold of that point can be detected. The light threshold at a point of the visual field increases, the photosensitivity decreases, which may indicate a visual field defect at this point. It

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is easy to find out regional defect in the visual field via static test, but the test time is long and complicated, while automated perimeter makes the automation and standardization possible in the threshold operation and the tracking of a patient’s response, which greatly improves the comparability of different test. After completing the threshold visual field test by computer automated perimeter, it will automatically compare each point’s measured values and the corresponding normal values at the same age, via ways such as digital dB value printout, gray scale, and probability graph to show to us the result of the visual field.

3.2.3.3 Superthreshold Test, Screening Test In a certain stimulus intensity of cursor within sight of the cursor, which belongs to superthreshold stimulus, and if cannot see the superthreshold that should be visible in an isopter area, then there may be something abnormal (such as isopter indentation or partial scotoma). Superthreshold tests, screening tests are often used in the screening of glaucoma or disease of the nervous system, which can quickly find some obvious damage of visual field, and then put it into the dynamic or static test for further diagnosis. 3.2.3.4 Testing Methods No matter whether through instrumental detection or commonly clinical face-to-face detection method, in fact, the basic principle all belongs to static, dynamic, and threshold test; only the detection results are more direct from automatic perimeter and it has a powerful follow-up analysis software. There are many methods of perimetry. Face-to-Face Test It is the easiest way. Doctors and patients are 1 m apart, face to face, both eyes remain at the same level, the patient’s left (right) eye toward the doctor’s right (left) eye. Cover the two corresponding eyes, then doctors put his fingers in the middle of two people from various peripheral directions to the center, when the patient perceived finger, he/ she immediately informs. If the doctor’s visual field is normal, then the patient can see the ­fingers

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at the same time as the doctor in all aspect, which means that the patient has a normal field of vision. This method is simple, but the accuracy is poor. Perimeter Test (Fig. 3.1) Using perimeter to examine the field of vision is more accurate, which include dynamic test and static test. Currently, the static test is used often, such as the Humphrey fully automatic computer vision perimeter. The most widely used Humphrey perimeter is the full threshold program. Firstly, enter the patient’s name, date of birth, patient number, degrees of glasses (near and distant vision), and pupil diameter on the computer. Then select a test, such as 24–2, 30–2, macular threshold tests, generally tests the 24–2 threshold, that is, the central 24 degrees. The test points tend to be a bit thinner and the number is large, but the test time is long and the patient is tired and unable to concentrate, and the result is inferior to the one with fewer test point. As a result, the 24–2 threshold test is the most popular one, especially the FastPAC, which only needs 6  min to complete. The 24–2 threshold test and 30–2 threshold test both can choose FastPAC, but it cannot conduct contrast test on glaucoma hemifield test (GHT). The SITA-Fast came out in 2001 is faster, 24–2 threshold only takes 3 min to measure each eye, and preserves GHT. In a very quiet darkroom, placing your head on the forehead bracket and the chin rest, the tested eye looks against the fixation at the center of perimeter dome, and the head shall not be tilted. Adjust the patient’s seat or perimeter height properly to make them comfortable. Cover the other eye with an eye mask. Depending on the age of the patient to add proper “reading addition” (add) on the lenses, which are placed on the frame of the perimeter with the lenses being close to the eyelashes and respond to the center. When patients are more than 30  years old, additional reading glasses are possibly needed. Commonly, we added +1.0  D with people aged from 30 to 39  years, +1.5  D from 40 to 44  years; +2.0  D from 45 to 49 years; +2.5 D from 50 to 54 years, and + 3.0 D for people above 55 years. For exam-

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ple: 50-year-old patients wearing −4.00 D glasses required −4  +  2.5  =  −1.50 (D) to examine the visual field. People under the age of 30 can wear glasses with distant vision. Tell the patient: “Look at the yellow center point, don’t move, when you see another flash point, immediately press the button. If you shilly-­ shally slightly a little bit later to press the button, the computer will think that you did not see the bright spot. If you want to have a rest, then it must hold down the button until you want to continue to do so. If you want to blink, then you must hold down the button on as well. Sometimes the spot is bright and easy to see. But be careful, sometimes the flash is very dark. Be careful to look at it, but your eyes are staring at the central yellow point without moving.” For patients who tested for the first time, it is better to use the instructional procedure to let the patient have a try, or it will often be full of tricks and cannot be used as a baseline record. During the test, the visual field technician should monitor the patient’s eyes through the TV or telescope, whether the pupil is in the center of the target. If there is bias, the control handle should be adjusted horizontally and vertically to correct the chin position. It is a common occurrence that the upper eyelid is not fully raised. The visual field technician should constantly remind the patient to keep his eyes wide open.

3.2.3.5 Visual Field Recording In the Humphrey StatPac 2 program results, each eye for a page, there are 7 main parts. Visual field measurement is the subjective examination of patients, and the errors are frequent. It is necessary to pay attention to the two important rules in evaluating visual field test: high reliability (without XX markers), visual reduction of test points has repeatability (several times before and after the same test point threshold similar decrease). The Reliability of Visual Field Measurement How do doctors measure the reliability of this subjective examination? There are three indices available for reference.

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1. Fixation loss: At the central fixation point, 15.5 degrees the temporal side and 1.5 degrees the lower part lies the physiological blind spot. When the light target is projected there, the patient sees the visual sign, which is the loss of gaze, such as 1/30. This showed that the computer tested 30 times, of which 1 time the patient transferred gaze. If the fixation loss is ≥20%, it indicates that the test is not reliable. The record will show “XX” mark to remind you. 2. False positives: The machine sends out a moving sound, while there is virtually no projection light, and if the patient takes it for granted to press the button to say he sees the mark, it is false positive. In addition, if the false positive is ≥33%, it indicates that the test is not reliable, and there will be a “XX” mark. 3. False negative: In the previously seen test sites, the patient did not respond with more intense light. If the false negative is ≥33%, it indicates that the test is not reliable, and there will be a “XX” mark. Threshold Values The 24–2 threshold test has 54 test points, 30–2 threshold test has 76 test points, and the graph records the threshold of each test point, repeatedly tested value is in the bracket. The higher the threshold dB, the higher the sensitivity of the optic cells and their axons will be. The 4 central test points represent the region of 5 degrees from the injection point of view, with the highest sensitivity, where the threshold is as low as 0, then the central vision will be threatened or even seriously decreased. It should be noted that the area where the threshold equals 0 (or very low), its significance cannot be explained by morphological deviations. Grayscale Printouts Gray map divide into ten different gray levels to represent the corresponding light threshold. Total Deviation Total deviation map has two figures. Each number on the upper figure represents the difference

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between the threshold of each test point and the normal value of the age group. The downward figure is the probability of tracing graph, the black squares represent the probability of less than 0.5%, meaning that the test points are most likely to be abnormal, only less than 0.5% of normal people would have such a low threshold. Other probability