How does LASIK (laser eye surgery) work?
LASIK is primarily for distance vision problems. In nearsightedness (myopia), the eyeball is "too big" compared to the normal size. The cornea (the focusing element even more important than the lens of the eye) does not "know" this so it is focusing a more typical distance back into the eye -which is not far enough in the case of a myopic, "big" eyeball. So if you are myopic, you cannot see off at a distance but your near vision can be quite good.
LASIK works to correct the mismatch of corneal curve focusing and the greater actual distance back to the retina. It does so by thinning and flattening the curved surface of the cornea. This is done with with a laser just under a very thin superficial Corneal flap that is temporarily folded out of the way, then immediately replaced afterwards to stick and heal, preserving the natural surface. In effect, the cornea is being weakened in terms of optical strength so it takes longer to focus further back into the eye.
problem, though, is that this thinning is also weakening the cornea
structurally to at least some degree. The higher the myopic prescription, the
more thinning of the cornea is needed, and the more structural weakening of the
cornea results. That is why risk in LASIK is roughly proportional to the degree
of myopic prescription being treated.
_Written by J. Trevor Woodhams, M.D. - Chief of Surgery, Woodhams Eye Clinic