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Understanding the Eye

The key to understanding refractive surgery, whether it is CK, PRK, or LASIK is to understand how the eye works. Sharp, clear vision is the result of light rays passing through the cornea, pupil and lens and focusing directly upon the retina. If the cornea is not round, or it is too steep or too flat in relation to the length of the

eye, light rays focus either in front of or behind the retina resulting in "refractive errors" such as nearsightedness, farsightedness and astigmatism. Refractive surgery is a term for several procedures designed to treat these vision abnormalities. The cornea is the clear surface of the eye. Many people who are nearsighted place contact lenses on their eyes to improve the way the cornea focuses light. Refractive procedures simply are another way of improving the way the cornea focuses light. Refractive procedures are done on an outpatient basis with most patients returning to their normal activities the following day. Your doctor will help you decide which procedure or combination of procedures is best suited for you.

How well you see depends, in part, on the shape of your cornea. The cornea focuses light on the retina, which is at the back of the eye. In a normal eye, light is focused correctly onto the retina. When the cornea is not shaped correctly, the image may focus in front of, or in back of the retina, resulting in blurry vision. Sharp, clear vision is the result of light rays passing through the cornea, pupil and lens and focusing directly upon the retina.

Nearsightedness
Nearsightedness, or myopia, occurs when the cornea is too rounded. People with nearsightedness can see things close to them, but have difficulty seeing distant objects. With nearsightedness, the eye’s refractive power is too strong, or the eyeball is too long, thus forcing the image to be focused in front of the retina of the eye rather than upon it as would be with normal vision. When light focuses in front of the retina, near objects can be seen clearly, but far objects appear blurry. When LASIK is performed on nearsighted patients, the laser removes tissue to flatten the cornea.

Farsightedness
Patients with farsightedness, or hyperopia, have corneas that are too flat. People with farsightedness can see distant objects but have a hard time seeing closer objects. With farsightedness, the eye’s refractive power is too weak or the eyeball is too short, thus forcing the image to be focused behind the retina of the eye causing far objects to be seen clearly and near objects to appear blurred. To treat this condition, the laser beam is directed to remove tissue from around the center of the cornea, making it steeper.

Astigmatism
Astigmatism occurs in people whose corneas are not spherical or round enough. The normal eye is shaped like a basketball. The football-shaped or astigmatic cornea makes it difficult for light to focus on the retina. By changing the pattern of the laser's beam, the tissue is removed in one direction more than the other. Astigmatism can occur in combination with nearsightedness and farsightedness. Some degree of astigmatism does not negatively affect vision, and is of no visual consequence. People with small degrees of astigmatism are still candidates for LASIK.

Learn more about how the eye works so you can be better educated to make a decision about your vision correction. Check out our Internet Links page, or visit a vision correction specialist.

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