The Aging Eye: Researchers Aim To Stop the Clock

By JANE E. BRODY

AGING Americans expect more from their eyes these days than ever before. People in their 70's and 80's want to be able to drive, play cards, recognize people on the street, travel with their grandchildren, take advantage of senior discounts in the movies and read the books they missed while working full time.

But eyes have a way of aging that can render such expectations unrealistic. Far worse than the loss of visual acuity that prompts most middle-aged people to resort to magnifying lenses are sight-robbing diseases like glaucoma, cataracts, age-related macular degeneration, diabetic retinopathy and other retinal disorders that afflict tens of millions of Americans, usually after age 50.

The incidence of such potentially blinding disorders is increasing rapidly as the number of older people grows. Experts predict, for example, that by the year 2030, 6.3 million older Americans will develop macular degeneration, up from 1.7 million in 1995. It is a still-irreversible disorder that robs people of the central vision needed to drive, read, watch television, recognize faces, play cards or do any fine work. If Grandma Moses had had macular degeneration, her artistic talents would never have been noticed.

Fortunately, research is progressing on a number of promising new treatments, including low doses of radiation, and a combination of lasers and light-activated chemicals, both of which are used for some particularly hard-to-treat forms of macular degeneration. Other research is concentrating on how to stop toxins that damage the eye in glaucoma, and the genetics of several different eye diseases.

''Older Americans today expect to enjoy their retirement with the same visual capacity that they had in their younger years,'' said Dr. Harold Spalter, professor of ophthalmology at Columbia-Presbyterian Medical Center in New York. But, alas, as was apparent at a four-day seminar that Dr. Spalter chaired here last month, researchers are still a long way from knowing how to reverse most blinding eye disorders.

Still, major progress in understanding and treating these conditions -- and perhaps detecting them early enough to blunt their effects -- was evident at the seminar, organized by Research to Prevent Blindness, a New York-based voluntary organization. Unfortunately, though, many elderly Americans cannot afford the early detection procedures described at the seminar because Medicare and many other insurance programs do not cover such preventive measures.

For example, while insurance companies would routinely cover a visual field examination for a patient who already has glaucoma, most would not pay for this test for a person who has not yet experienced vision loss, when the disease process might be stopped without lasting vision damage.

Furthermore, an ongoing study of 2,520 men and women aged 65 to 84 in Salisbury, Md., has revealed that the usual eye chart test for visual acuity is inadequate to assess vision losses that interfere with the ability of elderly people to get around on their own, perform tasks of daily living and avoid accidents that can result in serious or fatal injuries. Rather, Dr. Sheila West, professor of ophthalmology at Johns Hopkins Medical Institutions, reported that tests for contrast sensitivity -- the ability to distinguish, say, a step from the one below it -- are more revealing of functional disability in older people.

''We have found that loss of contrast sensitivity is as important as arthritis and heart failure in determining loss of mobility in the aged,'' Dr. West said. She traced this loss to ''nonspecific retinal changes'' and the beginnings of cataracts, a gradual clouding of the lens of the eye that eventually obscures vision. However, early-stage cataracts are rarely recognized by those who have them and are often dismissed as inconsequential by eye doctors.

Sunlight, Dr. West said, is a major factor in the formation of cataracts, and the damage is cumulative. By assessing the exposure of study participants to sunlight, Dr. West and colleagues determined that for every 1 percent increase in exposure to ultraviolet-B light, the risk of developing cataracts rose by 10 percent.

''There is no threshold for sun-related damage, the dosage is cumulative and no group is immune to it,'' Dr. West said the study showed. She recommended that when out of doors, everyone -- starting in childhood -- should wear lenses that block ultraviolet light and a cap with a brim that shades the eyes.

Dr. M. Cristina Leske, head of preventive medicine at University Medical Center in Stony Brook, N.Y., and associates, identified other risk factors for cataracts. Through a five-year study of 764 patients, they found that Caucasians are three times as likely as blacks to develop cataracts. Those who take the gout medicine allopurinol face more than a two-fold increase in risk, and smokers have a 60 percent increase.

On the other hand, certain nutrients appear protective. The risk was 30 percent lower among those who took multivitamin-mineral supplements and nearly 60 percent lower among those who took a vitamin E supplement, a finding that is now being tested in a clinical trial sponsored by the National Eye Institute. Still another study of 247 women aged 56 to 71 conducted at Tufts University in Boston found that taking vitamin C supplements for more than 10 years reduced the risk of early cataracts by 77 percent and the risk of moderately advanced cataracts by 83 percent.

But while cataracts can usually be treated very successfully by surgically removing the damaged lens and replacing it with a synthetic lens implant, age-related macular degeneration, the leading cause of legal blindness in the elderly, has yet to yield to an effective treatment. Macular degeneration involves progressive damage to the cells in the center of the retina that are responsible for straight-ahead vision.

Early cases are often treated with lasers, which have the unfortunate side effect of destroying normal retinal cells as well as the damaged areas beneath them. Furthermore, after laser treatment, the vision-damaging tissue often grows back.

Dr. Dennis M. Marcus, an ophthalmologist at the Medical College of Georgia in Augusta, said that laser therapy usually cannot be used for the most severe form of the disease -- so-called wet macular degeneration, which involves the growth of leaky blood vessels beneath the central retina. Instead, he and his colleagues are testing low-dose radiation to destroy the blood vessels but spare the normal retinal cells. Thus far, 100 patients have been treated in a clinical trial that will eventually involve 500 people with wet macular degeneration. While it is too soon to evaluate the effectiveness of the treatment, Dr. Marcus said that he has seen no radiation-induced complications.

Another clinical study is testing a technique called photodynamic therapy. It starts with the intravenous administration of a photosensitive dye that collects in the damaging blood vessels that are growing beneath the retina. The eye is then exposed to laser light that activates the dye, destroying those vessels only. Dr. Joan W. Miller, an ophthalmologist at the Massachusetts Eye and Ear Infirmary, said that preliminary studies showed that the technique effectively closes off the leaky vessels in the majority of patients. And while these vessels reopen and leak in some patients, the treatment can be repeated, if needed, without harm to the eye.

Some seminar participants said the best hope for conquering blinding eye diseases was unraveling the sometimes complex genetics underlying many if not all of these conditions. Just last month, for example, a team of scientists announced the discovery of the first genetic link to age-related macular degeneration, which strikes 25 percent of Americans over the age of 65 and is the major cause of vision loss in the elderly. The researchers hope that by studying mutations in this gene they will gain an understanding of how the disease damages the eye, a means of identifying those at risk and methods of prevention and treatment.

Glaucoma, for example, usually involves elevated pressure inside the eye, leading eventually to the death of ganglion cells, the nerve cells that transmit information from the eye to the brain. This disease afflicts perhaps eight million Americans and causes blindness in 5,500 each year. Currently the only available treatment involves continual use of eye drops that reduce intraocular pressure. This only works if treatment is begun early.

Dr. Robert W. Nickells, an eye researcher at the University of Wisconsin in Madison, said, however, that ''new advances suggest that glaucoma could be treated during the second or even the third stage of the disease.'' The second stage involves the release of high concentrations of ''excitotoxins,'' amino acids that are toxic to nerve cells. Dr. Nickells said that several compounds that intervene in the formation of excitotoxins have been developed to treat other neurodegenerative disorders and may also prove useful in treating glaucoma.

As for the third stage, he and his colleagues have found in monkeys and rodents that ganglion cells succumb to a form of programmed cell death that appears to be controlled by three genes that act as a molecular switch. One of the genes, called bcl-x, prevents the fatal blow and might be harnessed therapeutically to override the cell death mechanism, Dr. Nickells said.

But discoveries about the genetics of eye disorders can sometimes raise more questions than they answer. For example, Dr. Fulton Wong of Duke University Medical Center reported that as many as 50 genes are believed to be involved in the progressive disease retinitis pigmentosa, which begins as night blindness and loss of peripheral vision and eventually destroys central vision, leaving people blind. Thus far, four genes have been identified, each with multiple mutations that may result in different aberrations of the condition. One of the genes that codes for the production of the visual pigment rhodopsin can exist in 92 different mutated forms, Dr. Wong reported.

This year alone, three genes for various forms of glaucoma have been identified. But Dr. Janey Wiggs, an ophthalmologist and geneticist at Tufts University School of Medicine in Boston, said: ''This is a very complicated disease, with maybe 20 or 30 genes involved. And finding genes is only the first step. Where and when is the gene required and how does it produce disease? Does it result in too much or not enough of a gene product or make a toxic product?''

Still, she and others expressed guarded enthusiasm for the prospects of gene therapy to treat various devastating eye diseases. ''The eye is accessible,'' she said. ''It can be given selective treatment, using the other untreated eye as a control to see how well the treatment is working.''

Dr. J. Timothy Stout, head of the division of ophthalmology at Children's Hospital in Los Angeles, said, ''The potential use of gene therapy is nearly limitless for the ophthalmologist.'' He and his colleagues are exploring in animals the potential of a so-called suicide gene to treat eye diseases that involve excessive cell division, such as intraocular proliferative disease, macular degeneration and diabetic retinopathy. Normally, most cells in an adult eye are not dividing. Using as a gene carrier a virus that infects only actively dividing cells, he introduces into the eye a gene that by itself is not toxic but that results in cell death when combined with the drug ganciclovir, which also does not harm normal cells. Thus, the treatment is specific for the proliferating cells involved in the eye disease.