Photorefractive Keratectomy

What is PRK?

As with other refractive eye surgery procedures for correcting nearsightedness, the goal of the PRK procedure is to flatten the central zone, or visual axis, of the cornea so that light rays passing through the cornea and the inner lens will be focused properly on the retina.

This procedure came into use following the approval by the Food and Drug Administration (FDA) of the Summit Excimer laser system in October 1995, and of the VISX system for performing the PRK procedure in March 1996. The approval, with restrictions, was granted only after intensive FDA evaluation of the PRK procedure for a period of almost 10 years.

How is PRK performed?

Step 1: Eye preparation
Before the procedure begins, a nurse or technician talks to the patient about any immediate health problems that may affect readiness for the procedure. Antibiotic and anesthetic eye drops are then placed in the eye to numb it and prevent infection. The eye is swabbed with a sterile solution. The eyelid is then propped open with a lid retainer, and a paper or plastic "mask" is placed over the eye to keep eyelashes out of the way. The final step before the procedure begins is marking the cornea with a blue "dye ring," which serves as a reference point for the surgeon throughout the procedure. Because the cornea is numb, most patients experience little if any discomfort during these pre-operative preparations.

Step 2: Creating the flap
The next step in the PRK procedure is to remove the epithelium, the ultra-thin, film-like protective outer covering of the cornea, from the central zone (visual axis). This can be accomplished with either the Excimer laser or a surgical instrument.

Step 3: The Excimer laser
The Excimer laser is then used to ablate, or vaporize, layers of corneal tissue in order to "sculpt" the cornea to the shape needed to achieve the degree of vision correction required. The sculptured area is less than the diameter of an average pencil eraser. Preoperative tests and the evaluation process determine the sculpture pattern. The data that was gathered is entered into a computer that is built into the Excimer laser system. The computer then calculates the sculpting pattern and directs the application of the laser under the guidance of the eye surgeon. The surgeon continually monitors the progress of the procedure through a microscope that is a part of the laser system.

The patient is asked to focus on a fuzzy red light inside the laser. As the doctor activates the laser, there is a "popping" or "tacking" sound. In addition, there is a slight odor similar to that of hair burning, but there is no discomfort for the patient. The number of laser pulsations will depend on the nature of the refractive vision problem that is being corrected. This phase of the procedure takes only a minute or so.

Step 4: Post-operative measures
When the procedure is complete, additional antibiotic drops are placed in the eye, and it may be covered with a plastic shield. For a short while after the procedure has been completed, the eye is numb from the anesthetic drops. As the numbness wears off, the patient may experience some sensitivity to light and a scratchy or dry sensation as though something is in the eye. This feeling usually goes away within a few hours. The patient must not drive home following the procedure.

The patient returns to the doctor’s office the next day for a post-operative examination. The doctor checks the eye to see if the cornea is healing properly. Vision is checked and, for most patients, will range from 20/20 to 20/40 depending on the number of corrections received. For some patients, vision may continue to improve for several weeks before stabilizing.

The patient may experience some discomfort for the first 24 to 48 hours following surgery. Vision may be blurred for 3 to 5 days while the epithelium that was removed from the central corneal zone heals. The patient may also experience glare, halos, shadows, and some ghost images for a few weeks. These are normally transient phenomena and should lessen with time and then fade away.