Health : Aging Eyes Get a Closer Look : Researchers Finally Are Focusing on a Problem Almost Everyone Faces by Age 60: Farsightedness
You’re 40, maybe 45. Probably not more than 50.
But even if you’re not quite there, the time will come when, as you try to focus on the newspaper, you find yourself thrusting the page farther and farther from your eyes.
Soon, your arm won’t be long enough to let you see the page comfortably. The situation could develop slightly differently, with headaches and episodes of dizziness, leading you to fear that something is seriously wrong.
Chances are, however, that you will simply be in the process of becoming a presbyope. At middle age, you will have a disease so common that, by age 60, it claims a nearly 100% incidence in the general population.
It is presbyopia , the scientific name for an age-related farsightedness so ubiquitous, inevitable and unavoidable--yet so open to relief with glasses or contact lenses--that medical researchers have scarcely been interested in it since about 1860.
Cut From Budget
The federal government’s National Eye Institute cut off the funding to its only major presbyopia research program a year ago, apparently because the disorder could not compete as a budget priority with research on potentially catastrophic, vision-threatening disorders like glaucoma, diabetic retinopathy and retinitis pigmentosa.
As a result, there is not even consensus yet on why presbyopia occurs and how it progresses. For technical reasons, it is difficult to study its sequence in living humans. Experimentation on cadavers is useless. And only one animal, the rhesus monkey, has a vision system similar enough to man to be of any use.
“It’s one of those nagging, common disorders,” said Dr. Robert Reinecke, of Jefferson Medical College and Wills Eye Hospital in Philadelphia. “It is so common that none of us seems to be able to escape it.”
But vision research experts now are starting to question the prevailing scientific belief that the disorder is so mundane and inescapable that it cannot justify concentrated research. They note that the nature of work in modern society is changing so that more and more blue- and white-collar jobs require extended periods of intense close work.
Nature of Work Changing
Just as important, perhaps, some experts--including James Sheedy, associate clinical professor at the UC Berkeley School of Optometry--say the nature of work is changing just as the Baby Boom generation is nearing the time in life when its members, in giant numbers, will begin to confront presbyopia.
To Sheedy and other vision experts, the combined effects of workplace changes and the big and aging Baby Boom population could challenge the prevailing, helpless acceptance of presbyopia.
The condition, researchers suspect, may be hastened or worsened by exposure to new technologies such as computers. Sheedy is at the forefront of such research, though he concedes the computer’s role in presbyopia is still not established.
“There is some reason to believe that (computer exposure) exacerbates presbyopia,” he said. “But there is not yet sound scientific proof of such.”
Some top experts in the field, however, suggest that presbyopic white-collar workers may be comparatively better off than far-sighted people engaged in such jobs as computer manufacture and repair. Even bifocal-wearing car mechanics and plumbers, they say, face occupational difficulties more severe than white collar workers may ever encounter.
As it was explained in a recent editorial in the journal Archives of Ophthalmology by Laszlo Bito, a professor of ocular physiology at New York’s Columbia University College of Physicians: “Even the best bifocals may not be of much help to someone working in a confined situation, such as under the dashboard of a car.”
Bito, perhaps the nation’s best-known medical expert in presbyopia, said effective research on the disorder may be prompted by economics. He estimates that presbyopia exacts a nationwide toll on productivity of 1% to 2%--possibly as high as 3%--though he concedes no study has been done to offer precise numbers.
“We talk about reading glasses and they are pretty good--for reading,” Bito said. “But if you are engaged in other industrial activities, like repairing engines, you are much more dependent on variable focus. You can’t design glasses for every profession.”
Bito’s sense of urgency about presbyopia is not universally shared by some ophthalmologists, who are preoccupied with concerns about other vision problems they consider more pressing.
A Question of Resources
It’s a question of resources to experts like Dr. Ronald Smith, a USC School of Medicine professor and expert on the Estelle Doheny Eye Hospital staff.
“I have (presbyopia), so I’m sympathetic to the problem,” he said. “There has not been a lot of research. But compared to other problems . . . I don’t think it ranks very high. . . . I would have a lot of trouble convincing the American Diabetes Assn. of the urgency of presbyopia. After all, people with diabetic retinopathy (a retinal deterioration that often leads to blindness) would love to be able to see well enough to need bifocals.”
Presbyopia involves a mechanical failure in a process that makes the human eye a wondrous device. Light enters the eye through the cornea, the amount regulated by the iris. The rays are focused through the lens, a thin, circular, elastic layer suspended by a network of tiny ligaments attached, trampoline fashion, on a ring of tissue called the ciliary muscle. After the light passes through the lens, it is formed into what the brain recognizes as an image by the retina.
In a normal, healthy eye, when a person switches from looking at something far to something close, the ciliary muscle automatically loosens the ligaments suspending the lens. That change in tension lets the lens assume a rounder shape and move slightly in the eyeball so it refocuses. This process, accommodation , occurs so automatically in young people’s eyes they are unaware of it.
“It’s amazing how it occurs,” said Smith. “It is an active process that allows people to see clearly at any distance.”
But sometime in the late 30s, something starts to happen to the accommodation reflex. There are conflicting theories why. Some researchers believe the lens gradually loses its ability to shed worn-out tissue, thickens and becomes rigid, rendering it unable to play its role in focusing. This theory now appears to have the greatest number of adherents.
Other experts, however, believe the problem is in the ciliary muscle and ligament system. Somehow, the muscles lose their ability to release tension on the lens so it can change focus. Still others believe a combination of the two problems may be responsible.
Whatever the reason, in most people in their 40s, accommodation starts to break down, subtly at first, so they can focus simply by holding the printed page farther away. Some people, those normally nearsighted, even find their reading vision improves for a time.
But within a few years, presbyopia progresses so it can no longer be ignored. “Essentially,” Bito said, “you could say that presbyopia is the condition when your arm is too short.”
For most people, the inability to focus on close materials can be resolved with glasses or contact lenses; bifocals may be in order. Wide technological changes have led to greater and greater sophistication in corrective lenses, progress so quick that glasses and contact lenses have become a changing marketplace.
Still, Bito, Sheedy and other experts agree, contacts or glasses are not as good as the original, healthy eye. Even in the best prescription lenses, the eye’s infinite variations in focus are replaced by one or just a few inflexible selections.
Lenses have come a long way. The frontiers with such approaches, report Sheedy and Dr. Perry Binder, associate clinical professor at UC San Diego and president of the National Vision Research Institute, include:
- Progressive addition glasses. Unlike bifocals or trifocals, which offer the wearer choices between two or three specific fields of focus, progressive addition glasses provide something more akin to a zoom lens. They provide a wider range of focusing than can bifocals, as wearers shift their view from the lens’ top to bottom. Unfortunately, this greater flexibility also can make these glasses tough to adjust to and sometimes difficult to use since the focus field changes so often across the lens.
- Multiple glasses, with each pair custom-designed for specific tasks. Though Binder said it is easy to get carried away with this concept, it is possible to design glasses for any specific task. A drapery hanger or a druggist--whose job requires quick changes of focus between objects close to the eye--may have one set of bifocals for work, another for reading and household chores and still another for athletics.
- Bifocal and even trifocal contact lenses. Though trifocal contacts are not yet on the commercial market, bifocals have begun to appear. But Sheedy and Binder agreed that bifocal contacts, so far, may be too much of a compromise for most people. Such contacts can be hard or soft, though, either way, users’ night vision often is impaired. Why? The compromise of putting two prescriptions on the same contact reduces the light entering the eye through the part of the lens reserved for each field of vision. Double vision and blurring are common complaints; many bifocal contact wearers find that one of the two vision fields is not focused clearly enough.
- Monovision contacts, in which two prescriptions would be fitted in a bifocal, divided so one vision field is placed on each eye. The eyes automatically tend to pick the appropriate field of vision and the brain concentrates on that focused image and ignores the blurred one. But monovision also has drawbacks, Sheedy said. The lenses are not considered safe for driving because of the quick focus changes that chore requires. Monovision also is not good for someone whose occupation involves close work like reading all day. “It really works well for a person like a salesman whose primary responsibilities are people interactions, with just occasional reading material,” said Sheedy, “or for someone who spends a lot of time in household tasks or shopping.”
Because all the lenses involve compromise, Bito and other experts are starting to seek what causes deterioration in the eye and how to prevent it. For example, it may be possible, Bito said, for a drug to stimulate the lens to avert tissue build-up that may ruin its focusing or prevent deterioration of its assisting muscle structures.
Binder said that at least one company is developing synthetic antibodies that would send a chemical signal to cells in the lens to stop growing new tissue. Chemically, more cells intended for the lens could be killed, thus, averting excess accumulation of lens tissue.
Though no surgical techniques have yet proven satisfactory, some alternatives have been attempted and at least one new operation in development may have promise, Binder said.
Surgery for presbyopia, he said, has involved such procedures as hexagonal keratotomy--similar to radial keratotomy, a controversial treatment for nearsightedness. In hexagonal keratotomy, a shallow incision is made in the cornea so its curvature changes and it starts to help in accommodation. Results of this experimental procedure, which has not been subjected to rigorous scientific evaluation, have been unreliable, said Binder.
Another Technique
A newer experimental surgery, radialthermal keratoplasty--also called RTKP--involves inserting a hot probe into the cornea and altering with intense heat small circles of tissue. The result: a change in the cornea’s focusing, similar to that achieved by hexagonal keratotomy. Binder disapproves of this procedure, saying the techniques that preceded it have proven not only ineffective and temporary but also dangerous, with the potential to damage the eye.
Binder said another experimental surgery--in which plastic intraocular lenses similar to those used in cataract surgery, may be implanted in the eye--may have more promise. A study of them is under way, seeking to gain certification from the U.S. Food and Drug Administration for firms to market the lenses.
He said surgical developments may lead to a procedure in which tiny holes would be made in the lens capsule itself. Defective lens tissue then could be removed and replaced by an artificial substitute. Binder said perfection of a successful technique for lens replacement is at least five years away.
But whether drugs, surgery or just better glasses are involved, change is almost inevitable, Binder and Philadelphia’s Reinecke agree.
“I think there should be something we can do about” presbyopia, Reinecke said stoically. “I suspect that there will be one of these days.”
