What is the cornea?

Understanding the cornea is essential for understanding how LASIK works.

What Is the Cornea?

The cornea is the clear, dome-shaped front surface of your eye. It's like a window that allows light to enter the eye and helps focus that light onto the retina.

Corneal Anatomy

Five Layers (front to back)

1. Epithelium (50 microns)
- Outermost protective layer
- Regenerates quickly (3-5 days)
- Removed in PRK, preserved in LASIK

2. Bowman's Layer (12 microns)
- Dense protective membrane
- Cannot regenerate
- Affected by laser treatment

3. Stroma (500 microns)
- Makes up 90% of corneal thickness
- Where LASIK reshaping occurs
- Collagen fibers provide strength

4. Descemet's Membrane (10 microns)
- Thin, strong layer
- Basement membrane for endothelium

5. Endothelium (5 microns)
- Single layer of cells
- Pumps fluid out of cornea
- Cannot regenerate

Corneal Function

Light Focusing

• Provides 70% of eye's focusing power
• Refracts (bends) light entering the eye
• Works with lens to focus on retina

Protection

• Shields inner eye from dust, germs
• Filters some UV light
• First line of defense

Why Corneal Shape Matters

• Normal shape: Light focuses on retina
• Too curved: Nearsightedness (myopia)
• Too flat: Farsightedness (hyperopia)
• Irregular: Astigmatism

LASIK reshapes the cornea to correct these focusing errors.