eye. layers cornealscleral layer (tunica fibrosa) uvea (tunica vasculosa) retinal layer (tunica...

Eye

Layers

• Cornealscleral layer (tunica fibrosa)

• Uvea (tunica vasculosa)

• Retinal layer (tunica interna or nervosa)

Cornea Sclera

Sheathsof nerve

IrisCiliarybody

Ciliaryprocesses

Choroid

Neuralretina

Non-nervousanterior portion

Retinalpigment epithelium

Supporting coat Vascular coat 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

Cornea

Anterior chamber

Lens

Schlemm’s canal

Ciliary muscle

Limbus

Ora serrata

Zonule

Posteriorchamber

Iris

Ciliary bodyand process

Vitreous body

Photosensitiveretina

Choroid

Sclera

Fovea

Opticpapilla

Sclera

Pigment epitheliumChoroid

Optic nerve

1

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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’smembrane

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

CorneaPosterior chamberAnterior

chamber

Lens

Sclera

Vitreous body

Laminacribrosa

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)

Limbal conjunctiva

Limbal stroma

Canal of Schlemm

Cornea

Posterior chamber

Anterior chamber

Trabecularmeshwork

Iris

Uvea

• Middle, highly vascular layer• Three components:

– Choroid– Ciliary body

• Ciliary processes• Ciliary muscle

– Iris

IrisCiliary 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

Cornea

Sclera

Lens

Corneal epithelium

Canal of Schlemm

Bulbar conjunctiva

Ciliary muscle

Oraserrata

Ciliary process

Vitreous

Hyaloideo-capsular ligament

Nuclear zone oflens

SphincterOf pupil

Dilatorof pupil

Iris

Anterior chamber

Posterior chamber

Cornea

Canal of Schlemm

Conjunctiva

Ciliary muscle

Sclera

Episcleraltissue

Episcleralvessels

IrisSphincter pupillae

Ora serrata

Hyaloidea

Lens

Zonula ciliaris

Ciliaryprocess

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

Posterior chamber

Aqueous pathway

Vitreous cavity

Iridocorneal angle

Bulbarconjunctiva

Canal of Schlemm

Anterior corneal epithelium

Substantia propriaIrisCornea Sphincter pupillae

Anteriorlensepithelium

Posterior irisepithelium

Lens fibers

Lens capsule

Zonulaciliaris Equator

of thelens

Ciliaryprocesses

Ciliarymuscle

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

Sclera

Lens

Ciliary muscle

Sphincterof pupil

Anterior chamber

Posterior chamber

Dilatorof pupil

Ciliary processes

Zonule

Ora serrata

Cornea

Ciliarymuscle,relaxed

Suspensoryligament

pulls (arrow)to flatten lens

Zonula fibers(= suspensory ligament)relaxed

Lens, relaxed and permitted toassume greater curvature byits own elasticity (arrow) andpulled forward by themeridional fibers

Aqueous humorMeridional fibersCircular fibers of ciliary muscle, contracted

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 Stroma of the iris

Pigment epithelium

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 opticaof the retina

Foveacentralis

Maculalutea

• 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 nucleiRod cell nucleus

Cone pedicleRod spherule

Horizontal cellBipolar cell

MÜller cell nucleus

Body of MÜller cell

Amacrine cell

Ganglion cells

Optic nerve fibers

Light

Inner limiting membrane

Rod

Cone

Bipolar neurons

Pigmented epithelium

Ganglion neuron

Optic nerve fibers to brain

Müllercell

Nucleiof ganglioncells

Nucleiof bipolarneurons

Nucleiof rods andcones

Direction of Light from Lens

ILMONFL

GCL

IPL

INL

OPL

ONL

R&CL

OLM

PE

Artery

Outer nuclear layer

Cones and rods

Choroid

Sclera

Inner nuclear layer

Ganglion cell layer

Nerve fiber layerInner plexiformlayer

Outer plexiformlayer

Pigmentepithelium

Venule

Arteriole

Melanocytes

Synthesis of melaninby RER, Golgi, andmelanosomes. Melaninabsorbs light after ithas sensitized thereceptor.

Ion transport by mito-chondria and membraneinvaginations.

Digestion, by lysosomalenzymes, of photo-receptor fragementsphagocytized bypigment epithelial cells.

Vitamin A transportand esterificationin SER.

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

Inner segment

Outer segment

Connecting structure (cilium)

m

e

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

Inner segment

MitochondriaCilium

Outer segment

Cone cell

Outer segments

CiliumMitochondria

Inner segment

Cone

Rod

Cilium

Basalbody

Rootlet

Rod Cell Cone Cell

Free-floatingdisks

Bipolar cells

• Extend from outer to inner plexiform layers

• Cell bodies lie in inner nuclear layer

Outernuclearlayer

Outer plexi-form layer

Innernuclearlayer

Inner plexi-form layer

Ganglioncell layer

ConeCone

Rod

Horizontal cellBipolarcell

Lateral pathway

Bipolarcell

AmacrinecellAmacrine

cell

Ganglioncell

To optic nerve

Verticalpathway

Light

Ganglion cells

• Give rise to optic nerve

• Processes form nerve fiber layer

• Cell bodies lie in ganglion cell layer

Outernuclearlayer

Outer plexi-form layer

Innernuclearlayer

Inner plexi-form layer

Ganglioncell layer

ConeCone

Rod

Horizontal cellBipolarcell

Lateral pathway

Bipolarcell

AmacrinecellAmacrine

cell

Ganglioncell

To optic nerve

Verticalpathway

Light

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: ??

Outernuclearlayer

Outer plexi-form layer

Innernuclearlayer

Inner plexi-form layer

Ganglioncell layer

ConeCone

Rod

Horizontal cellBipolarcell

Lateral pathway

Bipolarcell

AmacrinecellAmacrine

cell

Ganglioncell

To optic nerve

Verticalpathway

Light

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 nucleiRod cell nucleus

Cone pedicleRod spherule

Horizontal cellBipolar cell

MÜller cell nucleus

Body of MÜller cell

Amacrine cell

Ganglion cells

Optic nerve fibers

Light

Inner limiting membrane

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

NFL

GCL

IPL

INL

OPL

ONL

R&C

Pigment epitheliumCone cells

Ganglion cells

Fovea centralis

ILM

OLM

Normalright eye fundus

Retinal modifications

• Ora serrata

– Anterior scalloped margin of nervous portion of retina

Sclera

Ora serrata

Choroid

Epithelium

Ciliary extensionof retina

Retina with nerve elements

x150

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

Centralartery

Ciliary arteries andnerves

DuraArachnoidOptic nerve

Retina

Laminacribrosa

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

Anterior epithelium

Newly formedsecondary lens fibers

Nuclei of lensfibers forming“nuclear bow”

Equator

Posterior pole

Capsule

Equatorialepithelium

Primary lens fibers

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

Orbicularis muscle

Eyelashes

Conjunctiva

Tarsal plate

Meibomian glands

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)

Eyelashes

Sebaceous and sweat glands

Marginal fascicle of orbicularis oculi muscle

sclera

posteriorpole

anteriorpole

cornea

choroid

iris

ciliarybody

retina

lensopticnervepigment

epithelium

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

Anterior chamberIris

Lens

Ciliarybody

Vitreous

Fovea

Laminacribrosa

Zonulaciliaris

Ora serrata

Dura

Optic nerve P.P.

V.A.

A.P.Posterior chamber

Limbus

Ciliary muscle

Lateral rectus

Sclera

ChoroidRetina

Cornea

Conjunctiva

Canal of Schlemm

Medial rectus

Visual axis Optical (geometrical) axis

Pars iridicaPars ciliaris

Ora serrata

Pars opticaof the retina

Foveacentralis

Maculalutea

Nervefiberlayer

Ganglion cell layer

Internal plexiform layer

Internal nuclear layer

External plexiform layer

External nuclear layer

Photoreceptor layerConeRod

Pigment epithelium

Dir

ect

ion o

f lig

ht

Outer segment

Cilium

Inner segment

Outer rod fiber

Cell body

Inner rod fiber

Rod spherule