Photorefractive keratectomy (PRK) versus laser-assisted in-situ keratomileusis (LASIK) for myopia

Apr 18 2006

A new review of recent studies suggests two popular laser-assisted surgeries to correct nearsightedness are equally effective at restoring 20/20 vision six months to a year after the surgery.

However, LASIK patients tend to recover their vision faster than PRK patients, which may be part of the reason their number has grown rapidly since the late 1990s, said Dr. Alex Schortt and Dr. Bruce Allan of the Moorfields Eye Hospital in London.

LASIK patients also report less pain after surgery than PRK patients, although they tend to be more uncomfortable during the actual surgery, the researchers found.

Schortt says patients might prefer these "side effects" associated with LASIK, but "none of the individual studies included in this review demonstrated a significant [vision] advantage for either treatment," he said.

"There are cases for both procedures where LASIK would be best for one patient and PRK would be best for another patient," said Melissa Bailey, Ph.D., an optometrist at the Ohio State University College of Optometry. "It really depends on individual patient factors," such the thickness of tissues in the eye and severity of the nearsightedness, she said.

The review appears in the current issue of The Cochrane Library, a publication of The Cochrane Collaboration, an international organization that evaluates medical research. Systematic reviews draw evidence-based conclusions about medical practice after considering both the content and quality of existing medical trials on a topic.

Typically, the nearsighted eye is longer than usual from back to front. This shape causes the eye to focus on light from distant objects in front of instead of directly on the retina, the part of the eye that transforms light into the nervous system signals that make up vision. The misfocus blurs the appearance of far-off objects such as highway signs or faces seen at a distance in a crowd.

LASIK (laser-assisted in-situ keratomileusis) and PRK (photorefractive keratectomy) both use a laser to reshape the eye's cornea, which helps to focus incoming light, in people with nearsightedness. With PRK, the cornea is reshaped by using the laser to gently shave off microscopic layers of the cornea. In LASIK procedures, surgeons cut a flap in the cornea to remove excess tissue below and then replace the flap like a hinged door.

In their review of six high-quality studies comparing LASIK and PRK, Schortt and Allan found no significant difference in the number of eyes regaining 20/20 "perfect" vision six to 12 months after each type of surgery, regardless of how severe the nearsightedness was before surgery. The studies involved a total of 417 eyes, 201 treated with PRK and 216 treated with LASIK, with some participants having surgery only on one eye, or some having each eye treated with the different procedures.

The researchers found some evidence that a greater proportion of eyes lose some of their visual acuity with PRK compared to LASIK six months after surgery.

Vision lost after PRK may be due in part to a corneal "haze" produced by inflammation caused by the procedure, the reviewers say.

"The risk of significant haze after PRK is an important difference between these procedures," Schortt said, although he notes that none of the studies they reviewed included the use of an anti-scar drug called mitomycin C, which has been used successfully to cut back on postoperative eye haze.

Although Schortt and Allan said their conclusions are not new and are "consistent with current practice," they believe that patients should still be aware of how the procedures compare. Allan, a practicing surgeon, uses both LASIK and PRK with his patients.

"I think patients and doctors prefer LASIK to PRK because it has a shorter and less painful recovery time," Bailey said.

"These interventions are performed on healthy eyes and the vast majority of patients are under 60 years of age," Schortt said, noting that patients can still choose more conservative options such as glasses and contact lens to treat nearsightedness.

It is important that patients are informed about and understand the effectiveness, limitations, safety, complications and relative merits of these procedures," he said.