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
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