Eye Layers Cornealscleral layer tunica fibrosa Uvea tunica

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 Lens fibers Iridocorneal angle 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 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 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 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 x 150 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