How Does Lasik Work:
Typically, in a patient who is myopic or nearsighted, the light focuses in front of the retina (back layer of the eye) most typically due to one of two reasons: 1) either the eyeball is too elongated thereby the focused light falls in front of the retina or 2) the focusing power of the cornea (clear part at the front of the eyeball) is too much due to the steep curvature of the cornea. In either case, the laser can shave off some of the tissue from the center of the cornea, thereby changing its curvature and focusing power to allow the light to come into focus precisely on the retina. Alternatively, In a hyperopic or farsighted patient, the light focuses behind the retina due to 1) either the eyeball being too short, or 2) the curvature of the cornea being too flat, leading to a weakened focusing power of the cornea. In either case, the laser can correct the problem by removing some of the tissue from the surrounding parts of the cornea, and thereby "steepening" its central power and its focusing power, leading to a precise focusing of the light on the retina.
When the patient has astigmatism, the cornea is more of a "football" shaped. In those cases, the laser reshapes the cornea by removing tissue from some parts of the cornea to make the cornea more spherical in shape.