Ocular Anatomy

G. Wollstein, MDAssociate Professor

The eye

Diameter: 24mm• Anterior chamber: 3mm

deep, volume of 250μL•Posterior chamber: 60μL•Vitreous: 6.5mL

• Diameter: 24mm• Anterior chamber:

3mm deep, volume of 250μL

• Posterior chamber: 60μL

• Vitreous: 6.5mL

Tear Film

• Superficial oily layer– Made by Meibomian glands– Function: anti-evaporative agent

• Aqueous layer– Made by lacrimal and accessory

lacrimal glands– Function: provides smooth optical

surface, nutrients, immunoglobulins, oxygen

• Mucin layer– Made by goblet cell– Function: wetting agent

Cornea

• Oval shape- 12 mm wide- 11 mm high

• Varying thickness- Center: 0.55mm

- Limbus: 1mm • Radius of curvature:

8mm

Cornea

• Average power: 43 diopters

• Steepest centrally, flatter peripherally

• More curved posteriorly then anteriorly

Corneal Layers

Epithelium

Bowman

Stroma

Descement

Endothelium

Histology OCT

Corneal Epithelium

Constant turnover of cells- Stem cells located in

crypts adjacent to limbus

- Move centripetally and anteriorly

Anchored to basement membrane by hemidesmosomes

Bowman’s layer

Anterior most stroma Thickness: 8-14μm Randomly dispersed

collagen fibrils Cannot regenerate

[

Stroma

Composition:- Collagen fibers- Ground substance- Keratocytes

Stroma Fibrils arranged in

oblique and parallel lamellae

Individual fibrils run the entire diameter of the cornea

Spatial organization of the fibrils allows for transparency

Descemet’s Membrane

Basement membrane of the corneal endothelium

Made of type IV collagen

Thickens with age[

Corneal Endothelium

A monolayer of hexagonal cells

Cell density: 3000 cells/mm2

- Decreases with age Cannot regenerate- Loss of cells results in

corneal edema

Anterior Chamber Angle

• Formed between the posterior aspect of the cornea and anterior aspect of iris

• Opening of the drainage system– Trabecular meshwork– Schlemm’s canal– Collector channels– Ant. ciliary v.

Uvea

• Iris• Ciliary body• Choroid

Iris

Anterior border layer Stroma Dilator muscle Posterior pigmented

layer- Two layers of heavily

pigmented epithelial cells

- Melanin

Iris Innervation Dilator muscle: Primarily sympathetic

autonomic system Sphincter muscle: Parasympathetic system

Ciliary Body

Base inserts into the sclera spur via the longitudinal muscle fibers- Gives rise to the iris

Apex is bordered by the ora serrata of the retina

Ciliary Body - Functions Accommodation

- Controlling the lens curvature through the zonules

Aqueous humor formation- Ciliary body

epithelium Trabecular and

uveoscleral outflow

Lens• Diameter: 9-10mm• Ant.-post. width: 6mm• Power: 20 Diopters- Cornea: 40D

• The actively dividing lens epithelial cells are located just anterior to the equator of the lens

• The high refractive index of the lens results from a high concentration of alpha, beta and gamma crystalins in lens fibers

Choroid Thickness: 0.25mm

Highly vascularized layer

Fenestrated vessels- Primary metabolic

source for the RPE

Choroid “Spaghetti bowl”

Choroid - Vasculature Arterial supply: Long

and short posterior ciliary a. and anterior ciliary a.

Venous drainage: Channeled toward equator vortex veins -> ophthalmic v.

Bruch’s Membrane

• Separating between the choroid and retina• Created from the fusion of basement

membranes of the choriocapillaris and RPE• Play a critical role in preventing penetration of

abnormal vasculature into the retina

Retina

• Converts light stimuli into electrical impulse

• Clinical macula: Bounded by the vascular arcade

• Histological macula: >1 ganglion cell body

Retina

• Fovea: Avascular center of the macula

• “Center of vision”

Retina Multilevel

connections between photoreceptors and optic nerve

RPE A monolayer of hexagonal cells RPE cells in the macula are taller, thinner and contain

more and larger melanosomes Functions include:- Vitamin A metabolism- Maintenance of the outer blood retina barrier- Phagocytosis of the photoreceptor outer segments- Absorption of light- Heat exchange- Formation of matrix around the photoreceptors- Active transport of materials

Photoreceptors The outer segment

consists of discs connected to the inner segment by the cilium

Constant shedding of discs as exposed to light

High concentration of mitochondria in the inner segment to provide the energy requirements

Photoreceptors

Photoreceptor density is greater in the fovea than elsewhere in the retina

The only layers of the retina present in the fovea are the photoreceptors and Henle’s layer (outer plexiform layer in the fovea)

Photoreceptors Nuclei in the outer

nuclear layer Axons (cone pedicle

and rod spherule) in the outer plexiform layer

Inner Nuclear Layer Made up of the cell

bodies of the bipolar, horizontal and amacrine cells

Interconnect photoreceptors with each other and with ganglion cells

Initial steps of image processing

Muller cells

Extend from the internal to external limiting membranes

Nuclei in the inner nuclear layer

Provide support and structural functions for the retina

Inner Retina Ganglion cell layer- Cell bodies

Inner plexiform layer- Ganglion cells

dendrites Nerve fiber layer- Ganglion cell axons

Retina – Blood Supply

• CRA enter the eye through the optic nerve and bifurcate into 4 main branches

• Supply inner retina down to the inner nuclear layer

• Outer retina supplied by the choroidal vasculature

Cool picture!

Vitreous

• Constitutes 95% of the eye volume

• Main component: water (98%)

• The component that make vitreous viscous is hyaluronic acid

• No time to cover other important ocular and orbital structures

• Assembly of other important slides follows

Eyelids

Extraocular Muscles

Orbit

Orbital base

Arterial Supply

Venous Drainage

Orbital Cranial Nerves

The End