PRK

PHOTOREFRACTIVE KERATECTOMY (PRK) ALSO KNOWN AS ADVANCED SURFACE ABLATION

In the past, if you were one of the millions of people with a refractive error (i.e. light rays not focusing precisely on the retina) eyeglasses and contact lenses were the only options for correcting vision. But with the arrival of refractive surgery, some people may have their vision corrected through surgery. Photorefractive keratectomy (PRK) is one of several refractive surgery procedures used by ophthalmologists to permanently change the shape of the cornea to improve the way it focuses light on the retina.

PRK is an outpatient procedure, done under topical anesthetic eye drops. It takes about fifteen minutes. The epithelium, the outer cell layer of the cornea, is removed with a blade, alcohol or a laser. An excimer laser, which produces ultraviolet light and emits high-energy pulses, is used to remove a thin layer of corneal tissue. Your ophthalmologist enters your vision correction information in a computer and the laser beam vaporizes the surface of the cornea up to that precise depth. By breaking the bonds that hold the tissue molecules together, your cornea is reshaped, correcting the refractive error. Because no incisions are made, the procedure does not weaken the structure of the cornea.

More recent variations of PRK include procedures which replace the corneal epithelium after removing it with alcohol (LASEK) or an instrument with a blade similar to the microkeratomes sometimes used for LASIK (Epi-LASIK). Collectively, all three of these procedures are considered variations of surface ablation of the cornea, and in the literature any of them may be referred to as “advanced surface ablation”. All of these are essentially the same procedure and yield the same visual results, although visual recovery can be slower after LASEK and Epi-LASIK because the devitalized corneal epithelium is replaced after laser correction is applied.

Immediately following surgery the eye is patched or a bandage contact lens is placed on the eye. After PRK vision is blurry for 3 days to one week. It may take a month or longer to achieve one's best vision. Patients may be on eye drops for up to three months.

Possible complications of PRK surgery include under-correction, over-correction, poor night vision and corneal scarring, although permanent vision loss is very rare. In the 1990’s, concern over corneal haze formation and loss of surgical refractive effect led surgeons to limit PRK to patients with nearsighted corrections of -6 Diopters or less, but newer laser technology and the use of small, one time doses of the anti-metabolite Mitomycin C during PRK surgery (a concept developed by Dr. Talamo in the laboratory in the 1980's) have greatly expanded the range of PRK, as haze formation is now exceedingly rare no matter what the correction.

Many patients enter the evaluation process for laser vision correction with the impression that visual results after PRK are not as good as LASIK. This was true for high levels of correction 10 years ago, but is no longer. Recent peer-reviewed publications of visual results after PRK report results at least equivalent to (and in some cases, better than) LASIK for comparable levels of refractive error.

To be a candidate for the procedure you must have a stable and appropriate refractive error, be free of eye disease, be at least eighteen years old and be willing to accept the potential risks, complications and side effects of PRK. PRK is frequently recommended over LASIK for those patients who are at risk for eye trauma (active duty military personnel, certain athletes) or who have a corneal shape or thickness not appropriate for LASIK. Additionally, patients with very dry eyes, those who have a history of frequent corneal abrasions or who have had prior RK or other corneal surgery are often best suited to PRK rather than LASIK surgery.