A few years ago, cataracts were a major cause of blindness, particularly in those over the age of sixty. In this disorder, delicate protein fibers within the lens slowly change their nature, turning the lens cloudy, much in the way that an egg white goes milky as it cooks. Sufferers can still detect light, but their vision loses its clarity. They see vague shapes, almost as though they were looking through a frosted window.
Cataracts, the clouding-over of the lens, usually affect both eyes and one more than the other. They are so common in elderly people that almost everybody over the age of sixty-five has some minor sign, usually at the edge of the lens, which doesn’t greatly trouble the vision. Like aching backs and arthritic joints, cataracts are part of growing old. Fortunately, they are painless.
The other good news for victims is that in recent years eye surgeons have made enormous progress in treating cataracts. The operation, which takes one of several forms according to the condition of the lenses, lasts about an hour. The success rate is high – about 95 percent. One technique, using a freezing probe, removes the whole lens. In another, the opaque part is drawn out by suction. In a third, a high-speed vibrator breaks up the cataract so that it can be withdrawn through a hollow needle. Because the operation destroys part of the lens, a replacement is needed before the patient can see clearly again. Sometimes, the opthamologist prescribes thick glasses or contact lenses. In other cases, a permanent plastic lens is implanted in the eye.
If this is intended, the surgeon makes a precise calculation before the operation to decide what power of lens will restore normal vision. This involves measuring the curvature of the cornea, the front part of the eye’s tougher shell, and the length of the eye. Age is not a factor in cataract surgery, but the patient’s health may determine which technique is used. Surgeons have successfully used plastic-lens implants to restore the sight of 100-year-old patients.