PRK, or photorefractive keratectomy, preceded LASIK and was the first modern laser vision correction operation widely used. Although it is still much less popular than LASIK, PRK is still preferable for many patients, especially those unsuitable for LASIK due to a thin or irregular cornea. During PRK no corneal flap is created. The epithelium, the thin layer of cells on the surface of the cornea, is removed by one of several methods, leaving a well-defined round defect or abrasion, large enough to accommodate the laser treatment.
Once the epithelium is removed, the actual laser treatment is identical to that of LASIK, and the results of the two procedures are essentially the same. The main difference is in healing time. In PRK it takes several days to a week or more for the epithelium to regenerate and cover the ablated or lasered area. During this healing period, the patient wears a soft contact lens 24/7 that acts like a Band-Aid to cover the cornea and allow the new tissue to grow back. The contact lens is placed on the cornea by the surgeon at the completion of the laser treatment and goes a long way in preventing pain and keeping the patient comfortable.
Besides the longer healing time, haze is another potential disadvantage of PRK over LASIK. Haze, an inexplicable cloudiness in the cornea, can develop months or even years after a perfectly performed PRK and can reduce vision to varying degrees. Haze is thought to be due to substances secreted by regenerating cornea tissue, and anti-inflammatory drops used for a month or more after PRK can usually prevent haze from developing. If haze does develop, these same drops are usually successful in eliminating it. Haze is more common in PRK treatments for prescriptions over –6.00, and for these patients, an anti-haze medication, mitomycin C, can be used during PRK to prevent haze.