DEAR DOCTOR K:

I've worn glasses and contact lenses for years. I just scheduled LASIK surgery. What will happen during this procedure?

DEAR READER:

LASIK is a type of eye surgery for people, like you, who want to avoid wearing glasses or contact lenses. How does it work?

To answer that, let's talk about how you see. You see things because the light from those things travels into your eye. First, it travels through the outermost, clear round layer of your eye, the cornea. The cornea bends light a little. Then light hits the lens inside your eye, where it gets bent some more. Finally, the light lands on the retina, in the back of your eye. That's the part of the eye that first "sees" something. If light gets bent properly by the cornea and lens, the retina sees things in focus.

The problem, of course, is that many people develop problems focusing properly. I think that eyeglasses were one of the most important inventions in human history: Imagine the problems we would have if huge numbers of us couldn't see clearly.

Glasses and contact lenses bend light so that it focuses on your retina. LASIK does the same thing, by reshaping your cornea.

LASIK begins with an important pre-surgery eye evaluation. At this appointment, your eye doctor will thoroughly examine your eyes. He will take precise measurements of your eyes, including measurements of the shape and thickness of your cornea.

On the day of the procedure, your doctor may give you a mild sedative to help you relax. Numbing eye drops are placed in your eye so that you won't feel pain or discomfort. An instrument is inserted into your eye to keep your eyelids open.

Next, a ringlike suction device is placed on the front of your eyes to hold your cornea in place. You'll feel a sensation of pressure, but no pain.

As the procedure begins, the eye surgeon uses a delicate cutting instrument to slice a small, hinged flap of tissue from the front of your cornea. You will not see or feel this. The surgeon then folds back the hinged flap of cornea.

Next, the laser is moved into position, and you will be asked to stare at a light. Staring fixes your gaze and keeps your eye from moving.

The doctor then uses the laser to reshape your cornea. The reshaping is guided by a computer. It is based on the precise eye measurements taken during your pre-surgery exam.

Finally, the doctor repositions the hinged flap of cornea. No stitches are necessary.

LASIK generally takes 10 to 15 minutes for each eye. You may feel slight discomfort or a burning sensation for a few hours afterward.

Many people who have LASIK surgery notice dramatic improvements in vision almost immediately. In others, improvement occurs gradually over three to six months. There's also a small chance you'll need to return for a second procedure to fine-tune your vision.

LASIK is not always perfect. It can cause side effects such as dry eyes and glare during night driving. But for almost everyone, it improves vision.

(Dr. Komaroff is a physician and professor at Harvard Medical School. Go to his website to send questions and get additional information: www.AskDoctorK.com.)

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