The FDA first approved lasers for human refractive correction in late 1997. Refractive errors include nearsightedness, or myopia, farsightedness, or hyperopia, and astigmatism, a football shape to the cornea, the clear, dome-shaped window of the eye. Patients qualifying for laser vision correction undergo the laser surgery on an outpatient basis. The perfected laser operation can be completed by an experienced ophthalmologist using only local topical eye drop anesthesia. The eye is held effortlessly open with a fine wire lid speculum, and the entire process is observed by the surgeon through a precision operating microscope.
Healing is rapid, and full recovery generally occurs within only a few days to weeks.
The excimer laser now used for this operation can be applied directly to the surface of the cornea, removing the surface cells or epithilium first. Next, the underlying stroma layer is shaped by the laser beam to neutralize, or correct, the refractive error by removing a thin wafer of central corneal tissue. Advantages of PRK include the convenience of an outpatient procedure, rapid recovery, a low rate of serious complications, and avoidance of significant structural weakness in the cornea. Disadvantages include some cases of slightly blurred vision at night and rare scarring, both of which often resolve with time and eye drop therapy. The major disadvantage of PRK is the mild to moderate pain experienced by many patients immediately following the operation, prior to healing of the surface defect.