Aug. 4, 2000 — For years, eye doctors have been treating people who would otherwise need reading glasses by using two different prescriptions of contact lenses — correcting one of the patient’s eyes for close-up tasks and the other for distance vision.

Now they are taking this concept further and using laser surgery to do the same thing. The idea may make some people a bit queasy, but doctors say the key to success is giving patients a detailed explanation of what to expect and plenty of support through the adjustment phase.

This type of correction is called monovision. It is used to treat a condition called presbyopia, usually seen in people 45 and over, in which the eyes gradually lose their ability to focus on nearby objects. Refractive surgeons — who specialize in correcting focusing errors such as nearsightedness, farsightedness, astigmatism, or irregularly shaped corneas — perform the procedure during standard laser eye surgery.

“In monovision, one eye is primarily used at a time for ideal focus,” refractive surgeon Andrew I. Caster writes in his book The Eye Laser Miracle. “Both eyes are used all the time, but one is generally primary, depending on the distance of the viewed object. Peripheral vision and depth perception are usually normal.”

Caster, who practices in Beverly Hills, Calif., tells WebMD that a trial run with contact lenses is “by far the best thing” before moving on to surgery. He estimates he has performed monovision correction in more than 1,000 patients. “If a patient chooses monovision and is educated about it in the proper way, they are almost always happy with it,” he says.

Andrew Maxwell, a refractive surgeon at the California Eye Institute in Fresno, Calif., estimates that he and his colleagues have performed the procedure on 300 to 400 patients. “The patient satisfaction level goes all the way from being extremely pleased to having a hard time dealing with the difference between the two eyes,” he says, but “in general, the patient satisfaction is relatively high.”

Like Caster, he says patients should try monovision with contact lenses first to see how they adjust. “About 25% of our patients were already living that way [with contact lenses], so they know if it’s something they want to do,” he tells WebMD.

Maxwell routinely offers the surgery to patients over 35, but he actually doesn’t recommend having it done before age 40. “Think of the eye as a camera. [To get a sharp image] the lens has to focus at a distance. The eye must do that, also. As you get older, that is harder to do. Monovision is a way of dealing with that.”

Speaking at the World Refractive Symposium last month in Miami, Maxwell presented his results with monovision surgery on 129 patients who had the procedure last year. The patients ranged in age from 40 to their early 60s. After the surgeries, Maxwell and his staff followed their progress for an average of about three months.

“Our best candidates are patients 40 to 55 years of age,” he says. Six patients asked to have the surgery reversed. Of those six, four were over 55. “Older patients didn’t adapt as well, possibly because they need a stronger reading prescription, which creates a greater difference [in prescription strength] between the eyes,” he says. “They also tended to be more satisfied with reading glasses.

“Nobody has demonstrated any significant loss of function or depth perception,” he says. “It’s just that some patients feel out of balance and don’t like it.”

Maxwell and Caster both emphasize that educating the patient on what to expect is essential. “The patient must understand that one eye is for near, one is for far, and the near eye will not be able to see clearly far away,” says Caster. “That’s the down side to monovision. It does not eliminate the need for glasses all the time, but it might reduce the need to 10% of the time.”

“We explain that this is a compromise,” Maxwell says. “We’re trying to provide [the patient] with the best chance of having some function without having to put on spectacles. It’s not perfect.

Still, he says, “monovision is a viable option for the well-informed patient. “