Wednesday, April 21, 2004

Patients who undergo laser-eye surgery during hot, humid weather are more likely to need follow-up treatments than those who have the procedure done during cold, dry weather, a new study shows.

“This is the first study to show that environmental factors can affect Lasik outcome,” said Dr. Keith Walter, assistant professor of ophthalmology at Wake Forest University in Winston-Salem, N.C. He led the research published Monday in the Journal of Cataract and Refractive Surgery.

Lasik, which is short for Laser-Assisted In Situ Keratomileusis, is a procedure to correct vision that involves changing the shape of the cornea by sculpting it with an ultraviolet laser.

In a telephone interview yesterday, Dr. Walter said up to 16 million people worldwide have had Lasik surgery to correct nearsightedness. About 1 million Americans undergo Lasik yearly, he said.

Prices typically range from $500 to $1,500 per eye.

Dr. Walter said he’s long suspected environmental conditions might influence the results of Lasik surgery.

“We use a very precise laser, which will always cut a piece of plastic perfectly. But when we use the laser to cut the cornea, which is biological tissue, we get a little variability in the cuts, so it’s not the laser that’s messing things up,” he said.

For his study, Dr. Walter analyzed data from Lasik surgeries he performed on 368 eyes. He determined that 15.5 percent of cases needed a second procedure to fine-tune vision.

“I looked at the data and found that patients who were undercorrected were ones I did during the summer. I found that outdoor humidity before the surgery was the most significant factor” in determining the need for additional surgery, he said.

Dr. Walter said increased humidity causes the cornea to “swell a little,” and, as a result, the laser “has to cut more water,” which can affect the clarity of vision.

He said his study shows that a 10 percent rise in treatment-room humidity meant an additional nine out of every 100 patients needed more treatment.

Even with those glitches, he stressed that “90 percent [of Lasik-treated eyes] still got excellent results” with the therapy, which was extremely popular in the past decade. Other research has shown that about 1 percent of Lasik patients suffer permanent complications, such as dry eyes and poor night vision.

Dr. Walter said he found that September was the worst month for Lasik surgery, with 50 percent of eyes requiring an additional treatment. No eyes that underwent Lasik during the drier winter months needed further surgery.

“Our study doesn’t mean that consumers should avoid Lasik surgery during the summer,” the eye specialist said, adding: “But they should make sure that their physicians compensate for temperature and humidity.”

Doctors can do that, he said, by allowing “a little more time and power” for the laser procedure.

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