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 鈥渄efocus鈥�.
Advertisement
In fact, the surgery can actually introduce new aberrations. 鈥淲ith standard
treatment you are increasing the amount of aberration,鈥� 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鈥檚 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鈥攁t least twice as good as
normal鈥攊n 16 per cent.
But because there can be aberrations in the lens as well as the cornea, this
method doesn鈥檛 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. 鈥淭he first technique gives us the optics of the eye as
a whole and the second technique gives us the shape of the eye,鈥� 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. 鈥淚 don鈥檛 see healthy people being treated this way.鈥�
Mrochen also points out that true super-vision requires more than surgery.
You also need a perfect retina and visual cortex.