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Eye Layers • Cornealscleral layer (tunica fibrosa) • Uvea (tunica vasculosa) • Retinal layer (tunica interna or nervosa) Cornea Sclera Ciliary body Iris Neural retina Non-nervous anterior portion Sheaths of nerve Supporting coat Ciliary processes Choroid Vascular coat Retinal pigment epithelium Retinal coat Refractive media • • • • • Cornea Lens Suspensory ligament (Zonule) Aqueous humor Vitreous body Chambers/body • Anterior chamber • Posterior chamber • Vitreous chamber Accessory structures • Eyelid • Lacrimal apparatus • Extrinsic eye muscles Schlemm’s canal Cornea Limbus Anterior chamber Lens Zonule Ora serrata Posterior chamber Ciliary muscle Iris Ciliary body and process Vitreous body Choroid Photosensitive retina Optic papilla Sclera Fovea Sclera Pigment epithelium Choroid 1 2 3 4 Optic nerve Cornealscleral layer • Cornea (anterior 1/6 of eye) – Epithelium – Bowman’s membrane – Substantia propria – Descemet’s membrane – Endothelium Corneal epithelium Bowman’s membrane Substantia propria Descemet’s membrane Corneal endothelium Cornealscleral layer • Sclera (posterior 5/6 of eye) – Dense fibrous connective tissue with elastic and collagenous fibers – Tendons of extrinisic eye muscles insert into this layer – Optic nerve region: sieve-like • Forms lamina cribrosa Scleral sulcus Anterior chamber Cornea Posterior chamber Lens Sclera Vitreous body Lamina cribrosa Limbus • Corneo-scleral junction – Corneal epithelium continuous with bulbar conjunctiva – Blood vessels that supply cornea – Endothelium • Spaces of Fontana: the trabecular meshwork • Canal of Schlemm: circumferential vessel that drains aqueous humor into episcleral veins (in limbus) Cornea Limbal conjunctiva Limbal stroma Canal of Schlemm Anterior chamber Trabecular meshwork Iris Posterior chamber Uvea • Middle, highly vascular layer • Three components: – Choroid – Ciliary body • Ciliary processes • Ciliary muscle – Iris Iris Ciliary body Zonule Choroid Choroid • Loose connective tissue • Richly vascularized • Pigmented • Several layers Ciliary Body • Girdles eye anterior to ora serrata • Triangular in shape in section • Two components: – Ciliary processes – Ciliary muscle Corneal epithelium Cornea Canal of Schlemm Bulbar conjunctiva Anterior chamber Sphincter Of pupil Ciliary muscle Dilator of pupil Iris Sclera Posterior chamber Lens Ciliary process Vitreous Nuclear zone of lens Hyaloideo-capsular ligament Ora serrata Cornea Sphincter pupillae Iris Canal of Schlemm Conjunctiva Ciliary process Ciliary muscle Sclera Episcleral tissue Episcleral vessels Zonula ciliaris Hyaloidea Lens Ora serrata Ciliary processes • Form the aqueous humor • Ciliary epithelium – Two layers • Deep, pigmented layer • Superficial non-pigmented layer (represents a non-nervous extension of the nervous portion of the retina anterior to the ora serrata) • Stromal cores with numerous capillaries Zonular fiber Epithelium Pigment layer Vessel layer Ciliary muscle Anterior chamber Aqueous pathway Posterior chamber Vitreous cavity Cornea Iris Sphincter pupillae Substantia propria Anterior corneal epithelium Canal of Schlemm Anterior lens epithelium Bulbar conjunctiva Posterior iris epithelium Iridocorneal angle Lens fibers Ciliary muscle Ciliary processes Zonula ciliaris Equator of the lens Lens capsule Ciliary muscle • Smooth muscle • Three sets of muscle fibers with different orientations • Important in accommodation – Contraction: releases tension on lens – Relaxation: increases tension on lens • Parasympathetic innervation Cornea Ciliary muscle Anterior chamber Sphincter of pupil Dilator of pupil Sclera Posterior chamber Zonule Lens Ciliary processes Ora serrata Cornea Aqueous humor Meridional fibers Circular fibers of ciliary muscle, contracted Zonula fibers (= suspensory ligament) relaxed Ciliary muscle, relaxed Suspensory ligament pulls (arrow) to flatten lens Lens, relaxed and permitted to assume greater curvature by its own elasticity (arrow) and pulled forward by the meridional fibers Iris • Anterior portion – Endothelial surface – Underlying connective tissue • Many pigmented cells: chromatophores • Amount of pigment determines eye color – blue eyes: little or no pigment – Gray, green, and brown eyes: increasing pigment – Smooth muscle • Sphincter: parasympathetic innervation • Dilator: sympathetic innervation Iris • Posterior portion – Heavily pigmented in all individuals – Two rows of cuboidal cells Sphincter papillae muscle Pigment epithelium Stroma of the iris Melanocytes Retina • Inner layer of eye; sensitive portion continues anteriorly only to ora serrata • Anterior to ora serrata continues as the non-nervous pars ciliaris • Ten named layers Ora serrata Pars optica of the retina Macula lutea Fovea centralis • • • • • • • • • • Pigment epithelium Rods and cones layer External (outer) limiting membrane Outer nuclear layer Outer plexiform layer Inner nuclear layer Inner plexiform layer Ganglion cell layer Nerve fiber layer Internal (inner) limiting layer Pigment epithelium Layer of rods and cones External limiting membrane Outer nuclear layer Outer plexiform layer Inner nuclear layer Inner plexiform layer Ganglion cell layer Optic nerve fiber layer Internal limiting membrane Pigmented epithelium Rod photoreceptor Outer limiting membrane Cone photoreceptor Cone cell nuclei Rod cell nucleus Cone pedicle Rod spherule Horizontal cell Bipolar cell MÜller cell nucleus Body of MÜller cell Amacrine cell Ganglion cells Optic nerve fibers Inner limiting membrane Light Direction of Light from Lens Optic nerve fibers to brain Nuclei of ganglion cells Ganglion neuron Müller cell Bipolar neurons Nuclei of bipolar neurons Nuclei of rods and cones Cone Rod Pigmented epithelium ILM ONFL GCL Artery IPL INL OPL ONL OLM R&CL PE Inner plexiform layer Outer plexiform layer Pigment epithelium Nerve fiber layer Ganglion cell layer Inner nuclear layer Outer nuclear layer Cones and rods Venule Arteriole Melanocytes Choroid Sclera Digestion, by lysosomal enzymes, of photoreceptor fragements phagocytized by pigment epithelial cells. Synthesis of melanin by RER, Golgi, and melanosomes. Melanin absorbs light after it has sensitized the receptor. Vitamin A transport and esterification in SER. Ion transport by mitochondria and membrane invaginations. Major retinal cell types • Photoreceptor cells – Rod cells – Cone cells • Bipolar cells • Ganglion cells Other cell types • Horizontal cells • Amacrine cells • MÜller cells Rod cells • 130 million • Intensity discrimination; night vision • Outer segment: rhodopsin – Rod-shaped; membranous stacks of disks contain pigment • Inner segment: organelles • Nuclear and synaptic regions • 100 rods supply each ganglion cell Synaptic body Nucleus m Inner segment e Connecting structure (cilium) Outer segment Cone cells • 6-7 million • Color perception and visual acuity • Outer segment: iodopsins – Conically shaped; membranous stacks of disks contain pigment • Inner segment: organelles • Nuclear and synaptic regions • 1-10 cones supply each ganglion cell Cone cell Inner segment Mitochondria Cilium Outer segment Outer segments Cilium Mitochondria Inner segment Cone Rod Rod Cell Cone Cell Cilium Basal body Rootlet Freefloating disks Bipolar cells • Extend from outer to inner plexiform layers • Cell bodies lie in inner nuclear layer Rod Cone Cone Outer nuclear layer Bipolar cell Outer plexiform layer Vertical pathway Bipolar cell Amacrine cell Horizontal cell Lateral pathway Amacrine cell Inner nuclear layer Inner plexiform layer Light Ganglion cell layer Ganglion cell To optic nerve Ganglion cells • Give rise to optic nerve • Processes form nerve fiber layer • Cell bodies lie in ganglion cell layer Rod Cone Cone Outer nuclear layer Bipolar cell Outer plexiform layer Vertical pathway Bipolar cell Amacrine cell Horizontal cell Lateral pathway Amacrine cell Inner nuclear layer Inner plexiform layer Light Ganglion cell layer Ganglion cell To optic nerve Other retinal cell types • Horizontal cells – Connect groups of cone cells in one area with rods and cones in another area – Probably integrate information between rods and cone • Amacrine cells – Primarily associated with ganglion cells – Function: ?? Rod Cone Cone Outer nuclear layer Bipolar cell Outer plexiform layer Vertical pathway Bipolar cell Amacrine cell Horizontal cell Lateral pathway Amacrine cell Inner nuclear layer Inner plexiform layer Light Ganglion cell layer Ganglion cell To optic nerve Other retinal cell types • MÜller cells – Retinal glial cells – Very large: stretch from internal to external limiting membranes – Supportive function Pigmented epithelium Rod photoreceptor Outer limiting membrane Cone photoreceptor Cone cell nuclei Rod cell nucleus Cone pedicle Rod spherule Horizontal cell Bipolar cell MÜller cell nucleus Body of MÜller cell Amacrine cell Ganglion cells Optic nerve fibers Inner limiting membrane Light Retinal modifications • Macula lutea – Lies in direct optic axis – ~ 5 mm in diameter – Rods gradually disappear – Cones become increasingly slender and numerous – Fovea centralis: entirely cones • ~ 0.6 mm in diameter • Clearest vision and greatest visual acuity ILM NFL Ganglion cells Fovea centralis GCL IPL INL OPL ONL OLM R&C Pigment epithelium Cone cells Normal right eye fundus Retinal modifications • Ora serrata – Anterior scalloped margin of nervous portion of retina Retina with nerve elements Ciliary extension of retina x150 Choroid Sclera Ora serrata Epithelium Retinal modifications • Optic disc – Forms the blind spot of the retina – Represents the retinal aspect of the optic nerve – Optic papilla: portion of disc that is slightly raised due to a heaping up of nerve fibers – Physiological cup: small central depression from which central artery and vein of retina emerge Central indentation of optic disc Central artery Retina Lamina cribrosa Ciliary arteries and nerves Optic nerve Arachnoid Dura Refractive media • • • • • Cornea Lens Zonule (suspensory ligament) Aqueous humor Vitreous body Lens • Capsule (a basal lamina; Type IV collagen) – Homogeneous; zonular fibers attach to it • Subcapsular epithelium – Single layer of cells on anterior surface – Transformed into lens fibers at equator Lens • Lens substance – Lens fibers (cells) – Older ones near center – Younger ones more peripheral • Aging of lens – Gradually loses water: becomes less elastic – Result is inability of lens to accommodate Anterior pole Capsule Anterior epithelium Newly formed secondary lens fibers Nuclei of lens fibers forming “nuclear bow” Equatorial epithelium Equator Primary lens fibers Posterior pole Zonule • Numerous fine fibers – Stretch from ciliary body to equator of lens – Thin collagen fibers and fibrillin Aqueous humor • Thin watery substance • Produced by ciliary processes Vitreous body • Clear, transparent gel; 99% water • Fills space posterior to lens • Contains collagen-like proteins plus hyaluronic acid Accessory structures • Eyelids • Lacrimal gland Eyelid • Tarsal plates: dense c.t.; support and strength to eyelid • Skeletal muscle: raises eyelid • Thin skin covers outer surface • Conjunctiva: a mucous membrane – Palpebral: 2 cell layers with goblet cells – Bulbar: continuous at limbus with corneal – epithelium Eyelid • Glands – Sebaceous glands • Meibomian – embedded in tarsal plates; inflammation produces a sty – Lubricate edges of lids • Zeis – Associated with hair follicles – Sweat glands (glands of Moll) • Eyelashes: 2-3 rows Skin Conjunctiva Orbicularis muscle Tarsal plate Meibomian glands Eyelashes Lacrimal gland • Compound tubuloalveolar gland • Serous secreting • Many myoepithelial cells Eye Eye Integument Serous tarsal gland Tarsus Orbicularis oculi muscle Conjunctiva Sebaceous tarsal gland (of Meibom) Marginal fascicle of orbicularis oculi muscle Sebaceous and sweat glands Eyelashes sclera anterior pole choroid posterior pole retina ciliary body iris cornea lens pigment epithelium optic nerve Eye terminology • Poles – Anterior: central point of corneal curvature – Posterior: central point of scleral curvature • Geometrical axis: anterior to posterior poles • Visual axis: center of pupil to fovea • Anatomical equator • Meridians: vertical and horizontal V.A. A.P. Posterior chamber Cornea Conjunctiva Anterior Canal of Schlemm chamber Iris Limbus Ciliary muscle Lens Medial rectus Zonula ciliaris Ciliary body Ora serrata Lateral rectus Vitreous Lamina cribrosa Sclera Fovea Dura Optic nerve P.P. Choroid Retina Visual axis Optical (geometrical) axis Pars iridica Pars ciliaris Ora serrata Pars optica of the retina Macula lutea Fovea centralis Nerve fiber layer Ganglion cell layer Direction of light Internal plexiform layer Internal nuclear layer External plexiform layer External nuclear layer Photoreceptor layer Cone Rod Pigment epithelium Outer segment Cilium Inner segment Outer rod fiber Cell body Inner rod fiber Rod spherule
