G. Wollstein, MD Associate Professor Ocular Anatomy G. Wollstein, MD Associate 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 Aqueous layer Mucin 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 Varying thickness Limbus: 1mm 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 Epithelium Bowman Stroma Descement Endothelium

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 Inner plexiform 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 Med and lat palpebral lig Levator palpebrae

Extraocular Muscles

Orbit

Orbital base

Arterial Supply

Venous Drainage

Orbital Cranial Nerves

The End