LASIK and Myopic Correction
As explained earlier, patients who are nearsighted have corneas with too much curvature in proportion to the length of their eyes. Once the corneal flap is made and lifted back, the excimer laser reshapes the underlying stroma to achieve a flatter cornea. The surgeon’s carful, precise measurements, which are programmed into the computer, guide the excimer laser. When the reshaping is complete, the flap is replaced. The result is that light rays coming through the cornea now come to a point of focus on the retina, rather than in front of it.
LASIK and Hyperopic Correction
Farsighted patients, on the other hand, have corneas that are proportionately too flat for the length of their eyes. The excimer laser is programmed to remove tissue from just the periphery of the stroma, leaving the middle untouched; this creates more of a domed shape. The increased curvature of the cornea will allow light rays to focus on the retina, rather than behind it.
LASIK and Astigmatism
To treat astigmatism, the excimer laser removes tissue in a somewhat oval fashion, adjusting the shape of the cornea in one direction more than the other. The goal is to produce a symmetrical surface so that light rays passing through the cornea at various places will meet at a single point of focus on the retina.
LASIK: State of the Art
No LASIK surgeon can promise 20/20 vision without the use of corrective eyeglasses or contact lenses. However, more than 99 percent of typical myopic patients who receive LASIK can see well enough to legally drive without glasses, usually by the morning after surgery. With today’s technological advances, the typical patient has a greater than 95 percent chance of achieving 20/20 vision.