A lens implant that can change focus like a natural lens promises to make cataract patients' eyesight almost as good as it was when they were young.The device, which is being developed by Jin-Hui Shen, an ophthalmologist at Vanderbilt University's School of Medicine in Nashville, Tennessee, contains six overlapping lenses.
As the muscles in the eye relax, the overlap increases, allowing patients to focus on closer objects.
Millions of people are given artificial lenses to replace their own lenses when they become clouded by cataracts. But these consist of a single, fixed-focus lens, so patients can only focus at a set distance.
He has now patented a device containing six overlapping lenses arranged like the petals of a flower.
Like other artificial lenses, the device would be inserted into the lens capsule fo the eye after the cloudy lens has been removed."It would be almost the same procedure," Shen says.
Flexible springs connect each lents to the edge of the lens capsule. When the rim of the device is squeezed by the relaxing eye muscles, the degree of overlap between the lenses increases, allowing the eye to focus on closer objects.When the muscles contract, pulling on the rim of the implant, the lenses spring back out again to allow focusing on more distant objects.
Shen has calculated accurately that these changes in the shape of the lens capsule should produce a focal range of 10 dioptres - as good as a healthy lens in a young person."In principle it could work," says George Waring, an ophthalmologist at Emory School of Medicine in Atlanta. But cells left behind after surgery can proliferate and cause the lens capsule to stiffen, he says. For variable focus lenses, this could be a problem.
If such trails are successful, they add, however, some patients might not need to wear glasses at all - unlike most elderly people, who gradually lose the ability to focus at different distances as the natural lens becomes more rigid with age.