Ophthalmologists improve LASIK

Ophthalmologists have developed a formula that slashes by nearly two-thirds the likelihood that patients will need repeat visits to an eye surgeon to adjust their vision after their initial LASIK visit. That's because the formula makes it more likely that surgeons will get it right the first time.

The new results, presented at the European Society of Cataract and Refractive Surgery meeting in London, are the result of a complex computer formula compiled by doctors and scientists at the University of Rochester Medical Center that takes into account myriad imperfections within the eye that weren't even known to exist a decade ago.

Even though most patients come out of refractive surgery with vision that is 20/20 or better, doctors have noticed that some patients exit the surgery slightly farsighted - not enough to seriously degrade their quality of vision or to require contact lenses or reading glasses, but enough to be a leading reason why people complain about the results of the surgery. A few others end up slightly nearsighted. While many of these patients still see at a level around 20/20, the slight farsightedness or nearsightednessis is one of the chief barriers preventing them from seeing even better, at a level around 20/16.

Eye surgeon Scott MacRae, M.D., of the University of Rochester Eye Institute presented the results showing a dramatic drop in farsightedness among LASIK patients. In a recent study where MacRae and colleagues used the formula, known as the University of Rochester Nomogram, during surgery, just six of 445 eyes or 1.3 percent were slightly farsighted after LASIK. He compared this to results from a previous study five years ago without the formula. In that study of 340 eyes, even though 91 percent of patients had 20/20 vision or better - the highest known percentage of any large study in the world at the time - 74 of the 340 eyes treated, or 21.8 percent, were slightly farsighted.

"Though those results were among the best anyone had gotten to date, we thought we could do better," said MacRae, who worked for two years with post-doctoral associate Manoj Venkiteshwar, Ph.D., to develop the formula.

While some doctors have noticed that patients are more likely to be slightly farsighted than nearsighted after LASIK, doctors have had no way to predict which patients would be affected, MacRae said. If a doctor adjusted all of his or her surgeries to avoid the problem, then the other 80 percent of patients would wind up slightly nearsighted.

The new formula takes the guesswork out of the picture and establishes a scientific basis for the phenomenon.

The software developed by Venkiteshwar and MacRae controls how the laser beam dances around the surface of the cornea during a LASIK procedure, allowing the surgeon to sculpt the cornea into just the right shape so that it produces as flawless an image as possible. During a procedure that typically might last anywhere from 15 to 60 seconds, the laser beam hits the cornea about 50 times per second, with generally 750 to 3,000 pulses. The timing and aim, controlled by both the surgeon and the software, have to be precise.