If you have read or heard much about LASIK, you may be familiar with the eye’s cornea, the clear front covering over the iris (colored part). But do you know how well-designed and efficient it is? The cornea has more than one job to do:
It must allow light into the eye unimpeded
It must protect the delicate eye structures behind it
It must bend (refract) incoming light towards a clear focus on the retina, the eye’s “camera film”
Three Main Layers All these layers are transparent. The cornea is a tough structure, although it looks delicate and certainly hurts if it is poked. It is continually replacing its own surface cells, the old ones being washed away by tears. The surface cells make up a top layer called the epithelium and this is where the LASIK flap is made before the LASIK laser corrects your vision.
The LASIK flap also includes some cells of the middle corneal layer, the stroma. The stroma does not replace itself continually and this is why laser vision correction, whether LASIK or an alternative procedure such as PRK or IntraLase, works on the stroma. It is a stable layer and your vision correction will be permanent.
The cornea does not need much oxygen and has no blood vessels, as they would block some of the incoming light. It is nourished by a fluid behind it called the aqueous humor (also transparent) which supplies oxygen and removes waste products. The cornea’s lowest layer, next to the aqueous humor, is called the endothelium. It is only one cell thick and if too much fluid builds up in the corneal layers, these cells pump it out into the aqueous humor. This keeps corneal water content steady and vision clear.
The Cornea is a Lens The eye’s crystalline lens sits behind the pupil, the black center opening in the iris. Light enters the eye through the cornea, travels through the lens, and continues on to the retina at the back of the eye. The cornea does about 60 percent of light refraction and the lens follows up with about 40 percent. Between them, in a 20/20 eye, they allow clear vision at all distances.
Corneal Curvature We are born with a certain curvature and contour on each eye’s cornea. If you are nearsighted, your corneas are curved too steeply. If you are farsighted, they are too flat. If you are astigmatic, your corneas are not spherical like a basketball, but oval like a football. These vision problems can all be corrected with a laser that reshapes corneal curvature.
You can learn more about eye structures and see what they look like at our video library.
If you would like to schedule a personal consultation with one of our eye doctors, please call or email us today. We have many locations in North Carolina for your convenience.
