This laser has been used for approximately 10 years, and more than a million of these surgeries have been done worldwide. However, the FDA did not approve this laser for use in the U.S. until 1996, so much of the early research and refinement of this technique was done in other countries.
PRK was first used to treat nearsightedness. In a nearsighted eye, light rays come to focus in front of the retina. By flattening the front surface of the eye, the cornea, the eye's natural focal point can be changed so that it focuses light more precisely on the retina. This is done by removing tissue from the center part of the cornea.
In a farsighted eye light rays come to focus behind the retina. The cornea needs to be more sharply curved in order to focus light rays on the retina and thus tissue is removed from the edges of the cornea in order to make it "steeper".
The technique of PRK involves removing the surface "skin" of the eye in order to expose the sturdy tissue underneath which gives the eye its shape. This is done using a local anesthetic eyedrop and is painless. This is different from LASIK in which a flap is cut in the cornea to expose the tissue underneath. The laser is then used to shape the underlying cornea in a procedure that usually takes one minute or less. For most patients having PRK, a protective contact lens is then placed on the eye, which allows the surface of the eye to reheal over a period of several days, and prevents most of the discomfort that might be associated with the recovery period.
Usually vision improves almost immediately, but during the recovery period vision is generally not as good as it would be with the best possible glasses or contact lenses. Once the protective contact lens is removed after several days, vision continues to improve and may be at its best level within approximately one week to one month after the surgery. Usually eyedrops are used on a frequent basis during the first 4-5 days to lubricate the eye, prevent infection and decrease any inflammation resulting from the surgery. Eyedrops are decreased rapidly over the upcoming weeks, though in some cases patients may use eyedrops for several months after surgery.
The success of PRK in eliminating the need for glasses or contact lenses is excellent. FDA research showed that 95% of patients had vision of 20/40 or better after surgery, and approximately 2/3 of patients had 20/20 vision. The proportion of patients who achieve "perfect" 20/20 vision is even greater at the lower levels of nearsightedness, while at higher levels of nearsightedness there is a somewhat larger proportion of patients where vision is vastly improved but does not reach the 20/40 level.
Risks of PRK are minimal. There is a small chance, as indicated in the statistics above, that postoperative vision may be dramatically better, but not equivalent to 20/20 vision. A small number of patients may have a weak pair of glasses that they use occasionally. The only other significant risk is that of a slight corneal "haze", which may restrict vision after surgery to slightly less than 20/20. This occurs in a very small percentage of cases and usually disappears on its own in a 3-6 month period. However, it may increase the chance of some difficulty with halos around lights at night or symptoms of glare in bright light. This haze or scarring is much more common when correcting higher levels of nearsightedness and very rare at lower levels.