How the Cornea Affects Your Vision
The cornea is the front surface of your eyeball. Often compared to the lens of a camera, it is a clear dome, and it is a fixed shape, meaning that it does not flex or bend when focusing. In LASIK surgery, small pieces of the cornea are removed to change its shape. About 65% to 75% of focusing occurs when light passes thorough the cornea. There are no blood vessels in the cornea, but there are lots of nerve endings. The cornea is very tough. The outer layer heals quickly, but if deeper layers are injured healing can be a lengthy and difficult process.
Bending Light
As light passes through the cornea, it is bent. This is called refraction. Refraction focuses the light on the retina so you can see clearly. If your eye is not quite the right shape, you have refractive error. Types of refractive errors include:
- Myopia – nearsighted
- Hyperopia – farsighted
- Astigmatism
LASIK and other surgeries, such as epiLASIK and PRK, reshape the cornea to correct refractive errors.
Layers of the Cornea
There are five, or possibly six, layers of the cornea. The discovery of a sixth layer, called Duo’s layer, was announced in 2013 and is a controversial subject among experts. The layers of the cornea are as follows:
- Epithelium. The epithelium is the surface layer. It is moistened by your tears. The cells regenerate quickly so this layer heals very fast. It acts as protection from the elements and minor injuries. Although it heals quickly, the slightest scratch is very painful due to the high concentration of nerve endings.
- Bowman’s. Bowman’s layer is very tough and the strong layer of the cornea that keeps your eye from bulging from the pressure inside of your eye.
- Stroma. The adjustments, made in LASIK and other laser vision correction procedures, are made to the stroma. It is the thickest layer.
- Descemet’s membrane. Thin barrier that protects against infection and injury. This layer regenerates and heals quickly.
- Endothelium. The innermost layer of the cornea pumps excess fluid out of the cornea. It is essential to maintaining clear vision because it prevents swelling of the cornea. Endothelial cells do not regenerate. Extensive damage to the endothelium can cause permanent vision loss and the need for corneal transplant.
- Duo’s layer. Extremely thin layer between the stroma and Descemet’s membrane. Some experts argue that it is not its own layer but a part of the stroma.
Learn more about your eyes and eye health by consulting with an ophthalmologist near you.
