Distinguishing PRK, LASIK And LASEK Eye Surgeries
By Stephanie Whyche
PRK, LASIK and LASEK. The names of these three refractive eye surgeries can look like alphabet soup. How do you make sense of them?
The purpose of all three of these surgeries is to reshape the cornea to correct such vision problems as nearsightedness, farsightedness or astigmatism. Such surgeries are called "refractive" eye surgeries because the cornea is reshaped so that it can better refract, or bend, light to focus images precisely on the retina.
PRK
The letters PRK stand for photorefractive keratectomy. The surgery was the first refractive eye surgery to use laser technology to change the natural shape of the cornea to correct a vision problem, Dan Durrie, M.D., says.
The surgery requires the surgeon to gently remove (not loosen and push aside) a thin layer of tissue from the outer surface or epithelium of the cornea. (The epithelium grows back in several days.) Then microscopic amounts of tissue on the surface of the cornea are vaporized (or ablated) with a special laser that emits pulses of cool ultraviolet light.
Dr. Durrie dubs this procedure "surface ablation," since it's tissue on the surface of the cornea that is removed to reshape the cornea. Dr. Durrie was on the team that carried out clinical trials on the excimer laser, for PRK surgery.
Over the years, however, PRK has had some problems, Dr. Durrie says. One is that healing varies widely from patient to patient, he says.
"We would take the skin off [the surface of cornea] and the skin would grow back in the next three to four days," Dr. Durrie says. "Some people would have to take a week off to have the procedure done and to heal. "In addition, with PRK there's a higher risk of postoperative infection and visual haziness.
LASIK
Enter LASIK eye surgery. LASIK, which stands for laser assisted in situ keratomileusis, came on the scene in the early 1990s. The U.S. Food and Drug Administration approved the use of the excimer laser for LASIK surgery in 2000.
Instead of using the laser to vaporize tissue on the surface (or epithelial layer) of the cornea, a thin flap is made in the cornea itself. The flap is opened like a hinged door, showing the stroma layer of the cornea. Then, using the excimer laser, the surgeon vaporizes small amounts of tissue inside the cornea. The amount of tissue vaporized depends on the vision problem and its severity. Afterwards, the flap is put back in place over the stroma, where, over a few months, it naturally reattaches itself.
"We left the skin on the eye. It was comfortable. Patients liked the idea that they could go in one day and see the next day without much pain," Dr. Durrie says.
But even cutting a temporary flap in the cornea comes with some risks and can lead to complications, Dr. Durrie says. Moreover, the visual outcome is not significantly better than PRK, and because of the variable wound healing, the refractive error could wind up being under- or overcorrected.
LASEK
Enter LASEK, laser-assisted epithelial keratectomy, "just the next step in photorefractive keratectomy or PRK," Dr. Durrie says.
In a way, researchers took PRK and fine-tuned it over the years, Dr. Durrie says. As with PRK and LASIK surgeries, an excimer laser is used in LASEK surgery. But LASEK differs from LASIK in that the corneal tissue that's ablated in LASEK is surface tissue, as it is in PRK surgery.
In LASEK, a thin layer of tissue on the surface of the cornea is loosened and is gently slid to the side before the reshaping of the cornea with the laser. The surface tissue that is pushed aside is ultimately repositioned back into place. In PRK surgery, the tissue on the surface of the cornea is removed completely. New tissue must grow back in that area.
LASEK has some potential advantages over PRK, Dr. Durrie says. Unnecessary loss of corneal tissue is reduced or avoided. There are no flap or flap-related complications, which in turn can increase the risk of corneal complications. This is especially true for people who have particularly thin corneas.
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