The cornea is the part of the eye that helps focus light to create an image on the retina. It is similar to the lens of a camera focusing light to create an image on film. If the cornea is not shaped properly, our eyesight becomes blurred or distorted.
People who are near-sighted have trouble seeing distant objects as clearly as nearer ones, and farsighted people have trouble seeing near objects. With astigmatism, the cornea's shape is so distorted that light is focused to two points. Laser surgery can address all of these by reshaping the cornea so that it can focus images properly on the retina.
The development of excimer lasers was critical to making laser eye surgery possible. Excimer lasers do not heat up the surrounding air or surfaces, so they can be precisely focused onto only the part of the eye to be treated.
By controlling the size, position and number of laser pulses, the surgeon can control how much of the cornea is removed. LASIK is the most popular method of eye surgery. The surgeon creates a "flap" in the outer tissue of the cornea and folds it back. Laser pulses are then applied to reshape the cornea. Then the flap is replaced, and conforms to the new shape. This speeds up the healing process.
What is 20/20 vision?
When eye doctors talk about "20/20 vision," they mean what an average person should be able to see when standing 20 feet away from a standard eye chart. This is "normal" vision. If you have 20/40 vision, when you stand 20 feet from the chart, you can only see what the average person sees standing 40 feet from it. If your vision is 20/10, you can see better than the average person: you can see at 20 feet what most people can see from 10 feet.