LASIK is eye surgery that permanently changes the shape of the cornea (the clear covering on the front of the eye) in order to improve vision and reduce a person's dependency on glasses or contact lenses.

See also: Corneal surgery

For clear vision, the eye's cornea and lens must bend (refract) light rays properly, so that images are focused on the retina. If the light rays aren't clearly focused on the retina, the images you see are blurry.

This blurriness is referred to as a "refractive error." It is caused by an imperfectly shaped eyeball, cornea, or lens. LASIK uses an Excimer Laser (an ultraviolet laser) to precisely remove corneal tissue to correct the shape for better focusing.

A complete eye examination will be done before surgery to make sure your eyes are healthy. Other tests will be done to measure the curve of the cornea, the size and position of the pupils, the shape of the eyes (to make sure LASIK is an option), and the thickness of the cornea (to make sure you will have enough cornea tissue left after surgery).

A signed informed consent form is needed before the procedure, confirming knowledge of the risks, benefits, alternative options, and possible complications.

LASIK is an outpatient surgical procedure and will take 10 to 15 minutes for each eye.

The only anesthetic used is an eye drop that numbs the surface of the eye. The procedure is done with the person awake. LASIK may be done on one or both eyes during the same session.

During LASIK, a special knife (a microkeratome) is used to cut a hinged flap of corneal tissue off the outer layer of the eyeball. The flap is lifted out of the way and a special laser is used to reshape the underlying corneal tissue.

The calculation for how much tissue is removed by the laser is done ahead of time. Once the reshaping is done, the surgeon replaces and secures the flap. No stitches are needed. An eye shield or patch will be placed over the eye to protect the flap and to help prevent rubbing or pressure on the eye until it has had enough time to heal.

LASIK is done most often on people who use glasses or contact lenses because of nearsightedness (myopia). It is occasionally used to correct farsightedness. It may also correct astigmatism.

FDA and American Academy of Ophthalmology developed guidelines and recommendations that detail who would be a good candidate for LASIK.

• You should be at least 18 years old (21 in some cases, depending on the laser used), since the vision of people younger than 18 usually continues to change. An exception is the small child with one very nearsighted and one normal eye. The use of LASIK to correct the very nearsighted eye may prevent amblyopia (lazy eye).
• You should not have this procedure if you are pregnant or breastfeeding since these conditions can affect eye measurements.
• You should not have this procedure if you take certain prescription drugs, such as Accutane or oral prednisone.
• Your eyes must be healthy and your prescription stable. If you're are nearsighted, you should postpone LASIK until your condition has stabilized. Nearsightedness may continue to increase in some patients until their mid to late 20s.
• You should be in good general health. LASIK may not be recommended for patients with diabetes, rheumatoid arthritis, lupus, glaucoma, herpes infections of the eye, or cataracts. You should discuss this with your surgeon.

Other recommendations:

• Weigh the risks and rewards. If you're happy wearing contacts or glasses, you may want to forego the surgery.
• Understand your expectations from the surgery. Are they realistic?

For patients with presbyopia, it's important to note that LASIK cannot correct vision so that one eye can see at BOTH distance and near. However, LASIK can be done to allow one eye to see near and the other far. If you can adjust to this correction, it may eliminate or reduce your need for reading glasses. In some instances, surgery on only one eye is required. If your doctor thinks you're a candidate, ask about the pros and cons.