If you find the information on Lasik on this site informative and have not done so already please assist us in maintaining and improving these sections by filling out the evaluation form linked at the bottom of this page Astigmatic correction Very frequently associated with nearsightedness is an oval cross section to the corneal surface, called astigmatism. Imagine looking through a lens that was distorted to provide more focus vertically than horizontally. Every oval has a short and long diameter 90 degrees away from each other. The axis of the short diameter, known as the treatment axis of the positive astigmatism could be vertical, or any other direction over the 360 degree surface.
Ophthalmologists use the former style, optometrists the latter.
Both are equally correct. Correction of astigmatism involves changing the profile of the laser beam during the corrective procedure. Instead of the round profile required for pure nearsighted correction, the equivalent of an oval beam profile oriented to neutralize the oval profile of the cornea is used. The intended result is a rounder, less oval corneal profile. The Visx Star laser is capable of correction of up to 7 diopters of astigmatism, but is FDA approved out to 4 diopters.