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 – 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 OCT Histology 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 - Aqueous humor formation - Controlling the lens curvature through the zonules 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