Anatomy and Physiology of the Cornea
🟢 Introduction
The cornea is the transparent, avascular, anterior-most part of the eye. It plays a vital role in vision by refracting light onto the lens and retina. Its unique structure and physiology are essential for maintaining ocular clarity and optimal visual acuity.
🔹 Anatomy of the Cornea
📍 Location and Features
• Forms the anterior one-sixth of the eyeball’s fibrous coat
• Continuous with the sclera at the limbus
• Transparent, allowing entry of light
🔵 Shape
• Elliptical when viewed from the front
• Thinner centrally and thicker peripherally
• Anterior surface more curved than posterior
🔹 Corneal Diameter & Thickness
• Horizontal diameter: ~11.7 mm (adults)
• Vertical diameter: ~11 mm (adults)
• At birth: 10 mm (nearly adult size), full size by age 2
• Posterior surface: circular, 11.5 mm
Thickness:
• Central: 0.52 mm (520 μm)
• Peripheral: 0.7 mm (670 μm)
• Refractive Power: 45 Diopters (75% of eye’s total refractive power)
Curvature:
• Central 5 mm = main refracting surface
• Anterior radius: 7.8 mm
•Posterior radius: 6.5 mm
🔹 Microscopic Structure of the Cornea
• The cornea has five layers (anterior → posterior):
1. Epithelium
• Non-keratinized stratified squamous (5–6 cell layers)
• Barrier against pathogens & injury
• Regenerates quickly
2. Bowman’s Layer
• Tough, acellular collagen layer
• Provides strength
• Does not regenerate if damaged
3. Stroma
• 90% of corneal thickness
• Collagen fibers + keratocytes
• Regular arrangement = transparency
4. Descemet’s Membrane
• Strong basement membrane
• Thickens with age
• Resistant to infection/trauma
5. Endothelium
• Single hexagonal cell layer
• Maintains dehydration & clarity via fluid pump
• Limited regeneration
🔹 Physiology of the Cornea
1. Transparency
• Due to collagen arrangement, no blood vessels, and relative dehydration (deturgescence).
2. Nutrition
• From aqueous humor (posterior), tear film (anterior), and limbal capillaries.
3. Oxygen Supply
• Mainly absorbed from atmosphere via tear film
• Additional from aqueous humor & limbal blood vessels
4. Sensory Nerve Supply
• By ophthalmic division of Trigeminal nerve (CN V)
• Extremely sensitive to touch, pain, temperature
5. Fluid & Ion Transport
• Endothelium pumps excess fluid to maintain clarity
• Epithelium also helps in transport
6. Healing & Regeneration
• Epithelium regenerates rapidly
• Stroma & endothelium have limited healing capacity
7. Blood Supply
• Cornea is avascular
• Small loops from anterior ciliary vessels (in periphery)
8. Nerve Supply
• Nerves lose myelin after 2 mm entry into cornea
• Form 3 plexuses: stromal, subepithelial, intraepithelial
Summary of lectures
• Cornea = transparent, avascular anterior eye structure
• Size: 11.7 mm × 11 mm, central thickness 0.52 mm
• Layers: Epithelium, Bowman’s, Stroma, Descemet’s, Endothelium
• Refractive power: 45 D
• Maintains vision via avascularity, collagen arrangement, and active fluid transport
• Essential for clear vision and ocular health
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