Clinical Anatomy
`of the Eye
`
`SECOND EDITION
`
`Petitioner - New World Medical
`Ex. 1008, p. 1 of 79
`
`

`

`Clinical Anatomy
`of the Eye
`
`SECOND EDITION
`
`Richard S. Snell, M.D., Ph.D.
`Emeritus Professor of Anatomy, The George Washington School
`of Medicine and Health Sciences, Washington, D.C.
`
`Michael A. Lernp, M.D.
`Clinical Professor of
`Ophthalmology,
`Georgetown University
`Medical Center, President, University of Ophthalmic
`Consultants of Washington, Washington, D.C.
`
`Illustrations by Ira Grunther, B.S.. A.M.I.
`
`Blackwell
`Science
`
`Petitioner - New World Medical
`Ex. 1008, p. 2 of 79
`
`

`

`1998 by Blackwell Science, Inc.
`Blackwell Science Ltd, a Blackwell Publishing company
`
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`required, the services of a competent professional should be sought.
`First edition published 1989 (ISBN 978-0-86542053-3)
`Second edition first published 1998
`11
`2012
`
`ISBN 978-0-6320-4344-6
`
`Library of Congress Cataloging-in-Publication Data
`
`Snell, Richard S.
`Clinical anatomy of the eye / Richard S. Snell, Michael A. Lemp.-2nd ed.
`p. cm.
`Includes bibliographical references and index.
`ISBN 978-0-6320-4344-6
`1. Eye—Anatomy 2. Eye-sockets--Anatomy. L Lemp, Michael A. II. Title.
`[DNLM: 1. Eye-anatomy & histology. 2. Orbit-anatomy & histology. 3. Cranial
`Nerves-anatomy & histology. 4. Eye Diseases—diagnosis. WW 101 671c 1997]
`QM511.S64 1997
`611'.84—dc21
`DNLM/DLC
`for Library of Congress
`
`97-39908
`CI P
`
`A catalogue record for this title is available from the British Library
`
`For further information on Blackwell Publishing, visit our website:
`www.blackwellpublishing.com
`
`Petitioner - New World Medical
`Ex. 1008, p. 3 of 79
`
`

`

`CHAPTER
`
`The Eyeball
`
`CHAPTE
`
`R OUTLINE
`
`133
`
`Fascial Sheath of the
`Eyeball (Fascia Bulbi,
`Tenon's Capsule)
`Function 133
`Clinical Notes 134
`Enucleation of the
`Eyeball 134
`Recession and
`Advancement of the
`Inferior Oblique and
`Inferior Rectus
`Muscles 136
`Surgical Removal of the
`Maxilla 136
`Herniation of Orbital
`Fat 136
`
`136
`
`The Eyeball
`General Shape and
`Dimensions 136
`Position 137
`Clinical Notes 138
`Exposure of the Eyeball
`to Trauma 138
`Displacement of the
`Eyeball 138
`Layers of the Eyeball 139
`Fibrous Layer 139
`Sclera 139
`Vascular Pigmented
`Layer 157
`Choroid 157
`Ciliary Body 160
`Iris 165
`Clinical Notes 174
`
`Nervous Layer—the
`Retina 175
`Pigmented Layer of the
`Retina 177
`Clinical Notes 180
`Clinical Notes 191
`Optic Nerve 192
`Structure 192
`Blood Supply 193
`Clinical Notes
`I 93
`Chambers of the Eyeball 194
`Anterior Chamber 194
`Posterior Chamber 194
`Aqueous Humor 194
`Intraocular Pressure 196
`Clinical Notes 196
`
`197
`
`Refractive Media of
`the Eye
`Lens 197
`Structure 197
`Suspension 202
`Accommodation 202
`Clinical Notes 202
`Vitreous Body 204
`Age Changes 206
`Functions 207
`Clinical Notes 207
`
`Clinical Problems
`
`Answers to Clinical
`Problems
`
`208
`
`210
`
`132
`
`Petitioner - New World Medical
`Ex. 1008, p. 4 of 79
`
`

`

`Fascia! Sheath of the Eyeball
`
`13 3
`
`Fascia! Sheath of the Eyeball (Fascia Bulb!, Tenon's Capsule)
`The fascial sheath is a thin membrane that envelops the eyeball and separates it
`from the orbital fat (Fig. 6-1). It thus forms a socket for the eyeball. The inner sur-
`face of the sheath is smooth and shiny and is separated from the outer surface of
`the sclera by a potential space called the twist-INT?! wire. Crossing the space and
`attaching the fascial sheath to the sclera are numerous delicate hands of connec-
`tive tissue, Attached to the outer surface of the fascia' sheath are coarse trabecu-
`be that run through the orbital fat.
`Anteriorly, the fascial sheath is firmly attached to the sclera about 1.5 f11171
`posterior to the corneoscleral junction. Posteriorly, the sheath fuses with the
`meninges around the optic nerve and with the sclera around the exit of the optic
`nerve. Close to the optic nerve the fascial sheath of the eyeball is pierced by the
`ciliary nerves and vessels (Fig. 6-2) and by the vortex (vorticosc) veins.
`The tendons of all six extrinsic muscles of the eye pierce the fascial sheath as
`they pass to their insertion on the eyeball (Figs. 6-1 and 6-2). At the site of perfo-
`ration the fascial sheath is reflected along the tendons of these muscles to form
`on each a tubular sleeve. The superior oblique muscle sleeve extends as far as the
`trochlea; the inferior oblique muscle sleeve extends to the origin of the muscle
`on the floor of the orbit.
`The tubular sleeves for the four recti muscles have important expansions.
`Those for the medial and lateral real arc strong and are attached to the lacrimal
`and zygomatic bones (Fig. 6-1). Because these expansions may limit the actions
`of these muscles on the eyeball, they are called the medial and lateral check liga-
`ments (Fig. 6-2).
`Thinner and less distinct expansions extend from the superior rectus tendon
`to that of the levator palpebrae superioris (Fig. 6-2), and from the inferior rectus
`to the inferior tarsal plate. Their exact functions are not known, although the
`superior expansion may ensure that the two muscles work in tandem when the
`individual looks upward. Similarly, the inferior expansion assists in pulling down
`the lower eyelid and maintaining an appropriate alignment of the lid with the
`globe when the person looks downward.
`The interior part of the fascial sheath of the eyeball is thickened and is contin-
`uous medially and laterally with the medial and lateral check ligaments (Fig. 6-2).
`This hammock-like arrangement of the fascial sheath constitutes what is known
`as the suspensory ligament (of Lockwood). This thickened area receives contribu-
`tions from the fascia of the inferior rectus and the inferior oblique muscles as
`they cross each other below the eyeball (see pages 249 and 252).
`
`Function
`The main function of the fascial sheath of the eyeball is to position and support
`the eyeball within the orbital cavity and permit the actions of the extrinsic mus-
`cles to produce movement of the eyeball. Very little movement takes place be-
`tween the eyeball and the sheath. Thus, the eyeball and sheath move together un
`a bed of orbital fat.
`
`Petitioner - New World Medical
`Ex. 1008, p. 5 of 79
`
`

`

`134
`
`6 / The Eyeball
`
`0
`
`Figure 6-1
`
`Orbital septum
`
`Periorbita
`Levator palpebrae superioris
`Fascial sheath of eyeball
`
`(A) Sagittal section of the
`orbit, showing the arrange-
`ment of the fascia around the
`eyeball and the extraocular
`muscles. Note the position of
`the suspensory ligament.
`(B) Horizontal section of the
`right orbit, showing the
`fascial arrangement. Note the
`check ligaments. Do not con-
`fuse the lateral palpebral
`raphe, which lies in front of
`the orbital septum and is part
`of the orbicularis oculi muscle
`(not shown), with the lateral
`palpebral ligament, which lies
`behind the orbital septum.
`
`Superior rectus
`
`t. Pe
`
`p Dula mater
`
`Suspensory
`ligament
`
`A
`
`fal
`
`, 2.
`
`
`Optic nerve
`
`cc,
`
`;
`
`.•.,:t•
`
`Inferior oblique
`
`friferior reCtuS
`
`Fascia!
`sheath of
`eyeball
`
`Medial palpebral ligament
`
`Orbital septum
`Lateral palpebral ligament
`
`Lacrimal part of
`orbicularis oculi
`
`Lacrimal sac
`
`Medial check
`ligament
`
`Orbital septum
`
`Lateral check
`ligament
`
`Fascial sheath
`of eyeball
`
`Medial rectus
`
`Lateral rectus
`
`Optic nerve
`
`B
`
`Periorbita
`
`Dura mater
`
`30' Clinical
`Notes
`
`Enucleation of the Eyeball
`In situations where it is necessary to remove the eyeball, the fascial sheath of the
`eyeball should be preserved to serve as a socket for the prosthesis. Because the
`extraocular muscles have fascial sleeves that are continuous with the sheath of
`the eyeball, the socket will then move when the muscles contract. An external
`prosthesis (glass eye) resting on the conjunctiva, over the socket, will also move
`to some degree as the socket shifts.
`
`Petitioner - New World Medical
`Ex. 1008, p. 6 of 79
`
`

`

`Fascia! Sheath of the Eyeball
`
`135
`
`Figure 6-2
`
`(A) Fascial sheath of the eyeball after removal of the eyeball. Note how the tendons
`of the extrinsic muscles of the eyeball, nerves, and blood vessels pierce the sheath
`to reach the eyeball. (B) Coronal section of the right orbit, showing the relationship
`of the fascia) sheath to the tendons of the extrinsic muscles—in particular, the su-
`perior rectus, the levator palpebrae superioris, the inferior rectus, and the inferior
`oblique. The black line representing the suspensory ligament has been excessively
`thickened to emphasize its presence.
`
`Superior rectus
`
`Superior oblique
`
`Ciliary nerves
`and vessels
`
`Lateral rectus
`
`Oti
`
`0
`
`Fascia( sheath of eyeball
`(Tenon's capsule)
`
`Lacrimal caruncle
`
`Medial rectus
`
`Optic nerve (fusion of
`fascia) sheath with
`meninges and sclera'
`
`Inferior oblique
`
`A
`
`Lateral check
`ligament
`
`Inferior rectus
`
`Conjunctiva
`
`Lateral
`rectus
`
`Levator palpebrae superioris
`Superior rectus
`Fascia) sheath of
`eyeball (Tenon's capsule)
`
`0
`
`Medial rectus
`
`Medial check
`ligament
`
`Eyeball
`
`B
`
`Inferior oblique
`
`Suspensory ligament
`Inferior rectus
`
`Petitioner - New World Medical
`Ex. 1008, p. 7 of 79
`
`

`

`I 36
`
`6 / The Eyeball
`
`The Eyeball
`
`Recession and Advancement of the Inferior Oblique
`and Inferior Rectus Muscles
`The close relationship existing between the suspensory ligament (thickening of
`the inferior part of the fascia) sheath of the eyeball) and the tendons of the infe-
`rior oblique and inferior rectos muscles makes operations on these muscles very
`difficult and the results unpredictable.
`
`Surgical Removal of the Maxilla
`Extensive removal of the maxilla for the treatment of malignant disease is not
`accompanied by sagging of the eyeball. The reason for this is that the suspen-
`sory ligament is strong enough to provide the eyeball with adequate support
`from below.
`
`Herniation of Orbital Fat
`The various extensions of the fascial sheath of the eyeball through the orbital fat
`to the bony walls of the orbital cavity assist the orbital septum in preventing her-
`niation of the fat into the eyelids.
`
`The eyeball is situated in the orbital cavity, a location that serves to protect it
`and provide a rigid bony origin for the six extrinsic muscles that produce ocular
`movement.
`
`General Shape and Dimensions
`The eyeball is made up of the segments of two spheres of different sizes placed
`one in front of the other (Figs. 6-3 and 6-4). The anterior, smaller segment is
`transparent and forms about one-sixth of the eyeball; it has a radius of curvature
`of about 8 mm. The posterior, larger segment is opaque and forms about five-
`sixths of the eyeball; it has a radius of about 12 mm.
`The anterior pole of the eye is the center of curvature of the transparent seg-
`ment, or cornea. The posterior pole is the center of the posterior curvature of the
`eyeball, and it is located slightly temporal to the optic nerve. The geometric or
`optic axis is a line connecting the two poles. The equator lies midway between
`the two poles (Fig. 6-4).
`The visual axis is a line connecting the fovea centralis of the retina with the
`nodal point of the eye and continuing anteriorly through the cornea. Remember
`that, because the fovea centralis is temporal and slightly inferior to the posterior
`pole, the visual axis and the optic axis do not coincide (Fig. 6-3).
`The anteroposterior diameter of the eye measures about 24 mm. Since the
`eyeball is slightly flattened in a vertical plane, the vertical diameter is about
`23 mm; the horizontal diameter, about 23.5 mm.
`The longer the anteroposterior diameter of the eye, the more myopic the eye
`is (i.e., light rays tend to be focused in front of the retina); conversely, the shorter
`the anteroposterior diameter of the eye, the more likely it is that the eye will be
`hyperopic (i.e., the light rays will be focused behind the plane of the retina). The
`actual focus is a result of a complex interplay involving the refracting power of
`
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`Ex. 1008, p. 8 of 79
`
`

`

`The Eyebati
`
`1 37
`
`110
`
`Figure 6-3
`
`Horizontal section through the eyeball at the level of the optic nerve. The optic axis
`and the axis of the eyeball are included.
`
`Anterior
`chamber
`
`Cornea
`Lens
`
`Pupil
`Iris
`
`Posterior chamber
`
`Ciliary body
`
`.•
`
`%!
`
`•
`
`Iridocorneal
`angle
`Conjunctiva
`Canal of Schlemm
`
`efr.,
`
`Sclera
`
`Ora serrata
`
`Suspensory
`ligament of lens
`
`Medial rectus
`tendon
`
`/
`
`Lateral rectus
`tendon
`
`Vitreous body
`
`Optic axis
`
`Retina
`
`Choroid
`
`Sclera
`
`Axis of eyeball
`
`Optic disc pi:
`Dura mater
`Subarachnoid space
`Optic nerve surrounded
`with pa mater
`
`M
`
`Fovea centralis
`
`it
`
`Lamina cribrosa
`Central artery of retina
`
`the cornea, which is dependent on its anterior curvature; the refracting power of
`the lens; and the length of the eyeball.
`
`Position
`The eyeball is situated in the anterior part of the orbital cavity, closer to the roof
`than the floor, and nearer the lateral than the medial wall. The orbital margins
`have a fairly constant relationship to the eyeball, Vertically, a straight edge
`applied to the superior and inferior orbital margins passes in contact with the
`cornea or slightly anterior to it. A horizontal straight edge applied to the lateral
`and medial margins reveals that about one-third of the eyeball lies anterior to it.
`Because the lateral orbital margin is the least prominent, it is consequently the
`lateral surface of the eyeball that is most exposed.
`
`Petitioner - New World Medical
`Ex. 1008, p. 9 of 79
`
`

`

`138
`
`6 / The Eyeball
`
`Figure 6-4
`
`(A) Diagram of the eyeball,
`showing the poles and the
`equatorial and meridional
`planes. (B) Diagram of the front
`of the eyeball showing the dis-
`tances between the insertions
`of the recti tendons and the
`corneoscleral junction or lim-
`bus. The seven anterior ciliary
`arteries are also shown. Note
`that there is only one anterior
`ciliary artery associated with
`the lateral rectus muscle.
`
`Equator
`
`/
`
`Anterior
`pole
`
`Posterior
`pole
`
`Meridian
`
`A
`
`Superior rectus muscle
`
`7.7 mm
`
`Lateral rectus
`muscle
`
`6.9 mm
`
`Anterior ciliary
`artery
`
`Medial rectus
`muscle
`
`3
`
`6.5 ram
`
`Inferior rectus muscle
`
`B
`
`it, Clinical
`Mies
`
`Exposure of the Eyeball to Trauma
`Although the eyeball is reasonably well protected by the surrounding bony orbit,
`it is protected anteriorly only from large objects, such as tennis balls, which tend
`to strike the orbital margin but not the globe. The bony orbit provides no protec-
`tion from small objects, such as golf balls, which may cause severe damage to the
`eye. Careful examination of the eyeball relative to the orbital margins shows that
`it is least protected from the lateral side. Rupture of the eyeball most commonly
`occurs from a blow directed from below and laterally.
`
`Displacement of the Eyeball
`A space-occupying mass within the cone formed by the extraocular muscles
`quickly causes forward displacement of the eyeball. An expanding mass outside
`
`Petitioner - New World Medical
`Ex. 1008, p. 10 of 79
`
`

`

`The Eyeball
`
`139
`
`the muscle cone has to be very large before displacement of the eyeball will occur.
`Moreover, the proptosis is usually asymmetric.
`
`Layers at the Eyeball
`The eyeball consists of three layers (Fig. 6-3), which from without inward are
`1) the fibrous layer, 2) the vascular pigmented layer, and 3) the nervous layer.
`
`Fibrous Layer
`The fibrous layer is made up of a posterior, opaque part, the sclera, and an ante-
`rior, transparent part, the cornea (Fig. 6-3).
`
`Sclera
`The sclera forms the posterior five-sixths of the eyeball and is opaque (Fig. 6-3).
`In the adult the sclera is white (see also Fig. 8-23). In children, when the sclera is
`thin, the pigment cells of the choroid show through, giving the sclera a bluish
`tinge. In the elderly the sclera may have a yellowish tinge from the deposition
`of fat.
`In the adult the sclera is about 1 mm thick posteriorly, thinning at the equator
`to 0.6 mm. It is thinnest, 0.3 mm, immediately posterior to the tendinous inser-
`tions of the recti muscles. At the corneoscleral junction the sclera is 0.8 mm thick.
`Anteriorly, the sclera forms the "white" of the eye and is covered with the fascial
`sheath of the eyeball and the conjunctiva. Posteriorly, the sclera is connected by
`delicate connective tissue to the fascial sheath of the eyeball. The outer surface of
`the sclera is smooth except where the tendons of the orbital muscles are attached
`to it (Fig. 6-4). The medial rectus inserts 5.5 mm posterior to the limbus; the infe-
`rior rectus, 6.5 mm; the lateral rectus, 6.9 mm; and the superior rectus, 7.7 mm.
`The insertions of the superior oblique and inferior oblique muscles arc posterior
`to the scleral equator (seep. 251).
`The sclera is perforated posteriorly about 3 mm medial and .1 mm above the
`posterior pole of the eyeball by the optic nerve. The site of this perforation is
`sometimes referred to as the posterior sclera, pramen. Here the sclera is fused
`with the dural and arachnoid sheaths of the optic nerve. Where the optic nerve
`fibers pierce the sclera it is weakened and has a sieve-like appearance and is
`known as the lamina cribrosa (Fig. 6-3). One of the openings in the lamina is
`larger than the rest and transmits the central retinal artery and vein, Since the
`lamina cribrosa is a relatively weak area, it can be made to bulge outward by a
`rise in intraocular pressure, producing a cupped disc.
`The sclera is also pierced by three groups of small apertures—anterior, mid -
`dle, and posterior.
`The anterior apertures are located at the insertion of the recti muscles and are
`for branches of the anterior ciliary arteries (Fig. 6-4). Each rectus muscle has two
`anterior ciliary arteries, with the exception of the lateral rectus muscle, which
`only has one.
`The middle apertures are situated about 4 mm posterior to the equator of
`the eye and number about four or five. These are for the exit of the vortex veins
`(Fig. 6-16).
`
`Petitioner - New World Medical
`Ex. 1008, p. 11 of 79
`
`

`

`1 40
`
`6 /
`
`Eyeball
`
`The posterior apertures arc small and numerous and are located around
`the optic nerve. They transmit the long and the short ciliary nerves and vessels
`(Fig. 6-16).
`Anteriorly, the sclera is directly continuous with the cornea, the line of union
`being known as the comeoscleral junction (or sclerocomeal junction or limbus).
`Just posterior to this junction, and lying within the sclera, is a circularly running
`canal called the sinus venosus sclerae (the canal of Schlemm). On section, this
`canal appears oval in shape and is lined with endothelium (Figs. 6-3 and 6-12).
`The outer wall of the canal forms a groove in the sclera. Posterior to the canal is a
`projecting ridge of sclera! tissue known as the scleral spur (Fig. 6-12). The scleral
`spur is triangular on section, with its apex pointing anteriorly and inward; it gives
`attachment to the ciliary muscle.
`
`Structure The sclera may be divided, for purposes of description, into three
`layers: 1) the episclera, 2) the sclera' stroma, and 3) the lamina fusca,
`
`Episclera The episclera is the outermost layer and consists of loose connective
`tissue. It is connected to the fascia] sheath of the eyeball (Tenon's capsule) by fine
`strands of tissue. It merges with the underlying scleral stroma. Anteriorly, the
`episclera has a rich blood supply from the anterior ciliary arteries, which form a
`plexus that extends between the extrinsic muscle insertions and the cornea-
`scleral junction. These vessels lie deep to the conjunctiva and normally are
`inconspicuous. However, in the presence of inflammation they become very red
`and congested (see p. 113). The episcicra becomes progressively thinner toward
`the back of the eye.
`
`Scleral Stroma This consists of dense fibrous tissue intermingled with fine
`elastic fibers (Fig. 6-5). The individual collagen fibrils (type I and type III) vary in
`diameter from 28 to 280 gm, with periodicities of 80 and 21µm. The bundles of
`fibrils run in. whorls, loops, and arches, and, although they are approximately
`parallel with the surface, many pass from layer to layer seemingly at random,
`forming a feltlike matting of the bundles (Fig. 6-6). The irregular arrangement of
`the collagen fibrils is largely responsible for the opacity of the sclera, in contrast
`to the transparency of the cornea where the fibrils run parallel with the surface.
`A few flat elongated fibroblasts are found between the collagen bundles (Fig.
`6-5), together with an occasional melanocyte.
`A viscoelastic structure, the sclera responds to a deforming force in a biphasic
`manner—a brief lengthening (elastic response) followed by a slow stretching
`(viscid response).
`
`Lamina Fusca This is the innermost layer of the sclera (Fig. 6-5). It is faintly
`brown, because of the presence of melanocytes, which form a thin, irregular
`layer. The lamina has many grooves, caused by the passage of the diary vessels
`and nerves. It is separated from the external surface of the choroid by a potential
`space—the perichoroidal space. Connecting the lamina fusca with the choroid
`are fine collagen fibers that provide a weak attachment between the sclera and
`the cho raid.
`
`Petitioner - New World Medical
`Ex. 1008, p. 12 of 79
`
`

`

`The Eyeball
`
`141
`
`Figure 6-5
`
`Photomicrograph of a section of sclera, showing the stroma and the lamina fusca.
`Nate the presence of elongated fibroblasts between the collagen bundles in the
`stroma. Note also the melanocytes in the lamina fusca. A small area of choroid
`packed with pigment cells is seen below. (Plastic section; H&E; x 400.)
`
`Scleral
`stroma
`
`41.
`
`Melanocyte
`in lamina
`fusca
`
`• lel ,
`
`
`
`ilk
`
`121".
`
`Fibroblasts
`
`Bundles
`of
`collagen
`fibers
`
`Choroid
`
`Blood Supply The sclera is a relatively avascular structure. However, anterior to
`the insertions of the recti muscles, the anterior ciliary arteries form a dense epi-
`scleral plexus. The posterior part of the sclera receives small branches from the
`long and short posterior ciliary arteries (Fig. 6-16).
`
`Nerve Supply The sclera is supplied by the ciliary nerves, which pierce the sclera
`around the optic nerve. The many short ciliary nerves supply the posterior por-
`tion, while the two long ciliary nerves supply the anterior region.
`
`Functions The tough, fibrous structure of the sclera protects the intraocular
`contents from trauma and mechanical displacement. The firmness and strength
`of the sclera, together with the intraocular pressure, preserve the shape of the
`eyeball and maintain the exact position of the different parts of the optic system.
`The strength and firmness of the sclera provide a rigid insertion for the extra-
`ocular muscles.
`
`Changes in Scleral Color with Age and in Disease The anterior portion of the
`sclera is visible clinically beneath the transparent conjunctiva, as the white of the
`eye. In the adult the sclera has a dull white color. In children, when the sclera is
`thin, the pigment cells of the underlying choroid show through, giving the sclera
`a bluish tinge. In the elderly, the sclera may have a yellowish color due to fatty
`deposits.
`
`1 10, Clinical
`\\ Notes
`
`Petitioner - New World Medical
`Ex. 1008, p. 13 of 79
`
`

`

`142
`
`6 / The Eyeball
`
`Figure 6-6
`
`Photomicrograph of a section
`of sclera, showing bundles of
`collagen fibers and nucleated
`fibroblasts. Note that many of
`the collagen bundles run par-
`allel with the surface, but
`considerable numbers are
`randomly arranged to form
`a feltlike structure. (H&E;
`x 400.)
`
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`411V ".
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`..480
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`
`In patients patients with osteogenesis imperfecta, Ehlers-Danlos syndrome, and other
`
`collagen diseases that produce a defect in collagen synthesis, the sclera is abnor-
`mally thin and is blue. The blue color, as explained above, is caused by the under-
`lying choroidal pigment cells showing through the thin sclera.
`It might be noted that the yellow appearance of the eyeball in jaundice is due
`not to pigment in the sclera but to bilirubin in the vascular conjunctiva.
`
`Thickness of the Sclera as a Factor in Cupped Disc,Tendoit Recessions and
`Advancements, and Trauma Sclera thickness varies considerably in different
`parts of the eyeball, the sclera being thinnest just behind the insertions of the
`recti muscles. In glaucoma, the raised intraocular pressure causes the lamina
`cribrosa to bulge outward. This is responsible for the development of the cupped
`disc in the chronic form of glaucoma.
`In strabismus, which is commonly treated with tendon recessions or advance-
`ments, it is important to remember that the sclera is very thin (about 0.3 mm or
`less) where the tendons are sutured to the sclera.
`A blow to the eyeball may rupture the sclera, usually at the sites of muscle
`insertion. Almost always this is associated with damage to the underlying cho-
`roid and retina.
`
`Perforations of the Sclera and the Spread of Neoplasms Wherever blood ves-
`sels and nerves pierce the sclera, the passage provides a pathway for the spread
`of intraocular tumors, such as melanomas, from inside the eyeball to the exte-
`rior. The most common site of extraocular extension of a tumor is along the
`optic nerve.
`
`Petitioner - New World Medical
`Ex. 1008, p. 14 of 79
`
`

`

`The Eyeball
`
`143
`
`Blood Supply of the Sclera, the Development of the Ciliary Flush, and the
`Healing of Surgical Incisions While the blood supply to the scleral stroma is
`poor, the episclera has a rich arterial supply. This is particularly important from
`the clinical point of view, in that an episcleral plexus—formed by branches of the
`anterior ciliary arteries—exists beneath the conjunctiva. Normally, this plexus is
`inconspicuous, but in the presence of inflammation involving the cornea, iris, and
`ciliary body, marked vasodilatation may occur, especially in the limbal area sur-
`rounding the cornea. This pronounced vasodilatation is known as a ciliary flush.
`The rich blood supply to the episclera results in rapid healing of surgical
`incisions.
`
`Nerve Supply of the Sclera and Eye Pain The sclera receives a profuse sensory
`innervation. It follows, therefore, that inflammations of the sclera will cause a
`dull, aching pain. Since the extraocular muscles are inserted into the sclera, the
`pain is made worse by ocular movement.
`
`Cornea The transparent cornea forms the anterior one-sixth of the eyeball (Fig.
`6-3 and Fig. 8-23). Because its curvature is greater than over the rest of the eye-
`ball, a slight sulcus, the sulcus sclerae, marks the junction of the cornea with the
`sclera. Seen from the front, the cornea is convex but somewhat elliptical in
`shape. Although the dimensions of the cornea vary considerably from one per-
`son to another, the approximate measurements are about 10.6 mm vertically hut
`about 11.7 mm horizontally. Posteriorly, the cornea is concave and circular,
`measuring about 11.7 mm in diameter. fhe cornea is thinnest at its center,
`measuring about 0.5 to 0.6 mm, and thicker at the periphery, measuring about
`0.7 mm.
`The radius of curvature of the anterior surface of the cornea is about 7.7 mm;
`that of the posterior surface, 6.9 mm. I Iowcvcr, it should be pointed out that it is
`frequently more curved in the vertical than in the horizontal planes (regular
`astigmatism).
`The cornea is the main structure responsible for the refraction of light enter-
`ing the eye. It separates the air, with a refractive index of 1.00, from the aqueous
`humor, with a refractive index of 1.33. (For further measurements, see Table 6-1.)
`
`Structure Microscopically, the cornea consists of five layers (Fig. 6-7). From front
`to back, they are 1) the epithelium, 2) Bowman's layer (membrane), 3) the sub-
`stantia propria, 4) Descemet's membrane, and 5) the endothelium.
`
`Epithelium The corneal epithelium is stratified and consists of five layers of
`cells (Fig. 6-8). Its total thickness measures about 50 to 60 pm. The superficial
`cells are flattened, nucleated, nonkeratinized squamous cells, and the deep-
`est cells are columnar. At the corneoscleral junction (limbus), the epithelium be-
`comes thicker and may consist of 10 or more layers of cells. Here, the epithelium
`becomes continuous with the bulbar conjunctiva. The corneal epithelium is
`devoid of melanocytes except at the limbus in dark races. The greater part of the
`epithelium is also devoid of the imrnunocompetent dendritic cells, Langerhans'
`cells; however, these cells are present in the peripheral corneal epithelium.
`
`Petitioner - New World Medical
`Ex. 1008, p. 15 of 79
`
`

`

`144
`
`6 /
`
`the Lyeball
`
`Table 6-1
`
`Important Measurements of the Human Cornea Used in Refractive Surgery
`
`Thickness (pM)
`Peripheral
`Central
`Refractive index
`Air
`Tear
`Cornea
`Aqueous
`
`Radius of curvature (mm)
`Anterior
`7.7
`Posterior
`6.9
`Central radius of curvature and refractive power
`7.7 mm = +43.6 D
`Air-tear
`Tear-cornea
`7.7 mm = +5.3 D
`Cornea-aqueous 6.9 mm = —5.8 D
`Total central refractive power = 43.1 D
`—
`- -
`Data from Holladay JT. Waring CO III. Optics and topography of radial keratotomy. In: Waring CO III, ed. Refractive keratotomy for myopia
`and astigmatism. St. Louis: Mosby, 1992:37-144.
`
`700
`540
`
`1 .00
`1 .336
`1 .376
`1 .336
`
`filt
`
`Figure 6-7
`
`Diagram showing structure of
`the cornea.
`
`12/311130DAC). — Corneal epithelium
`Bowman's membrane
`
`Substantia propria
`
`-
`
`Descemet's membrane
`Corneal endothelium
`
`The superficial cell layer is two to three cells thick (Fig. 6-8). They are flat, have
`horizontal nuclei, and are attached to one another by desmosomes. Electron
`microscopic examination of the outer surfaces of the superficial cells (Fig. 6-9)
`shows microvilli and microplicae (ridges) that extend into the superficial tear
`film. Some of the cells appear to be lighter and have many microvilli, while other
`darker cells have fewer microvilli and are centrally located. It is believed that the
`microvilli and microplicae of these surface cells assist in retaining the tear film
`and thus in keeping the cells moist. As the superficial cells age, they lose their
`attachments to one another and are lost in the tear film.
`The middle-zone cells are polyhedral in shape, with convex anterior surfaces
`and concave posterior surfaces (sometimes called wing cells). The nuclei are oval
`or round. Multiple desmosomes attach the cells to their neighbors. The lateral
`borders of the cells show many interdigitations, and the presence of numerous
`gap junctions permits free intercellular communication in this zone.
`
`Petitioner - New World Medical
`Ex. 1008, p. 16 of 79
`
`

`

`The Eyeball
`
`145
`
`Figure 6-8
`
`- •
`
`Cr
`
` Corneal epithelium
`Bowman's membrane or layer
`
`(A) Photomicrograph of a sec-
`tion of the cornea, showing
`the corneal epithelium; the
`clear Bowman's membrane or
`layer; the substantia propria;
`the narrow, clear Descemet's
`membrane; and the corneal
`endothelium. (H&E; x 260.)
`(B) Photomicrograph of a high-
`power view of the corneal
`epithelium. The epithelium is
`stratified, the deepest cells
`are columnar, and the super-
`ficial cells are squamous and
`nonkeratinized. Note the clear
`zone, beneath the epithelium,
`containing Bowman'