From four-eyes to super-eyes

IMPROVED techniques for corrective laser eye surgery could give people much better eyesight than those with so-called normal vision, say researchers in the US.

Jim Schwiegerling, an ophthalmologist at the University of Arizona in Tucson, says customised surgery could take patients to the theoretical limits of human vision. People would be able to pick out small objects from twice or maybe even four times as far away as those with normal or 20/20 vision. Fewer than 5 per cent of people are born with such super-vision.

Poor eyesight is caused not only by short and long-sightedness, but by asymmetries in the cornea and lens that distort images. But at the moment, laser surgery on the cornea corrects only major aberrations such as the cylindrical errors that cause astigmatism or the spherical errors that cause "defocus".

In fact, the surgery can actually introduce new aberrations. "With standard treatment you are increasing the amount of aberration," says Michael Mrochen, an ophthalmologist at the University of Zurich.

This is one of the reasons why only 60 per cent of those who have corrective surgery end up with 20/20 vision. Doing any better than this is a hit-and-miss affair.

So researchers are now looking for ways to measure more subtle aberrations so they can be corrected. One way to do this is to shine light into the eye and analyse the reflections bouncing off the retina. Recent trials by Mrochen's team suggest surgery based on this information can produce 20/20 vision or better in 93 per cent of cases, and 20/10 vision or better-at least twice as good as normal-in 16 per cent.

But because there can be aberrations in the lens as well as the cornea, this method doesn't reveal the exact shape of the cornea. So other groups are trying to improve results by using scans to directly measure the shape of the cornea. At the moment, laser surgeons take only a fairly rough measurement of the curvature of the cornea.

Schwiegerling, however, is going further. His team is the first to try to combine both approaches. "The first technique gives us the optics of the eye as a whole and the second technique gives us the shape of the eye," says Schwiegerling. Having such detailed information should make all the difference, he says.

Schwiegerling is developing a computer model that will use all this information to create a highly accurate picture of an eye to guide the machines that carry out laser surgery. The model will even try to take into account changes in shape during healing.

The aim, Schwiegerling says, is to ensure that everyone who has surgery gets 20/20 vision at the very least. But it will be two or three years before the technique is available. And, because of the risks inherent in any surgery, people with normal vision are unlikely to get a shot at having super-vision, he says. "I don't see healthy people being treated this way."

Mrochen also points out that true super-vision requires more than surgery. You also need a perfect retina and visual cortex.

Author: Duncan Graham-Rowe and Michael Le Page

New Scientist issue: 23rd June 2001

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