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- - - PART 2 The ding Eye If the eye is a camera, its photographic components lose precision with age. Nearly all the structures that bend, guide, and transform light entering the eye change with age some dramatically, some only slightly—reducing the amount of light reaching the retina. In fact, eye specialists have estimated that the retina of a 60-year-old typically receives one-third the light of a 20-year-old's retina. Light may be limited even before it strikes the cornea. Baggy or droopy eyelids, which may occur after age 40, cut down on available light. Thinning of the eyelids with age, for example, may cause skin from the upper lid to protrude like an awning over the eyelashes, restricting the field of vision. Or the lower lid may turn inward, rubbing against the eye and causing pain and tearing. If these conditions are serious, plastic surgery may be recommended to alleviate them. The aging cornea not only flattens, limiting the ability to focus, but may also be flecked with fatty deposits that reduce transmission of light. Increased scattering of light gives the cornea a yellowish tinge, reducing the Juster of aging eyes. The cornea also loses sensitivity to touch with age, so injury to the eye's protective surface may occur without pain or other warning. The smaller opening of the pupil with age, a condition known as senile miosis, markedly limits the amount of light falling on the retina. The disorder may be most serious in dim light, because the aging pupil's maximum diameter may only be one-fourth that of a younger eye. One possible benefit of the smaller diameter, akin to choosing the smaller Opening of a camera lens, is enhancement of depth of field~bjects both near and far are more likely to be in focus, although they appear dimmer. In fact, some older people may report improvement of eyesight. annar- _,~ ———~——- 7 ~ ~ entry due to smaller pupil size. Yellowing or clouding of the lens is another factor in reducing illumination. In addition, the yellowing lens also acts as a filter, absorbing more blue and violet light. This changes the perception of This section includes material from the presentations by David Michaels, Meredith Morgan, William Kosnik, Leon Pastalan, Sara Czaja, Chris Johnson, and Robert Sekuler at the Invitational Conference on Work, Aging, and Vision. ~3
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colors: white objects may appear yellow, and the distinction between blues and greens is decreased. Structural changes in the vitreous body, a large gel-like region that lies between the lens and the retina, have several implications for the elderly. In the aging eye, the vitreum liquefies and the gel portions clump together, causing spots, or floaters, to appear in the field of vision. The same change may trigger the vitreum to detach and pull away from the retina. The extra force may cause swelling of the macula, bleeding, or even detachment of the retina, resulting in severe impairment or loss of vision. Vitreous detachment is usually sudden, triggered by a jolt or other physical injury, and older workers exposed to large and frequent vibrations may be at high risk. Light reaching the aging retina encounters fewer nerve cells than it does in younger eyes. For example, the number of light-sensing cones in the most sensitive area of the retina (the fovea) may decrease dramati- cally between age 40 and age 60. This is believed to affect the clarity of eyesight. Electrical measurements of visual activity of the brain, re- corded from the scalp, appear to indicate that visual processing is slower in the elderly. Other age-related changes in the retina and the eye's nervous system are under study. No older patient is typical. Although only about 17 percent of elderly people are severely visually impaired, quality of vision varies widely. For example, 60 percent of older people have near-perfect (20/20) vision with eyeglasses; about 40 percent have 20/40 vision or worse, discerning only at 20 feet what a person with normal vision can still see at double the distance. A common problem among people over 40 is presbyopia, a gradual decline in the ability to focus on nearby objects and small print. The condition occurs when the lens of the eye hardens, losing the soft, pliable quality that enabled it to change shape for focusing. There is no cure, but eyeglasses and contact lenses help compensate for reduced vision. During their 40s and 50s people may change glasses every two years due to increased hardening of the lens. . . . . .. . .. Changing Eyesight: Significance for Daily Living One of the challenges in helping the older worker is determining the extent to which visual impairment affects both job performance and the quality of everyday living. Although there have been numerous studies on aging and vision, little of this research has examined the special problems of vision in the? wnrkul~f..~ Rent. ~t.lldi~ It that ~ ~ t~ ~ ~ v vat ~ ~ v . . ~ . . . . . a slowdown ot the visual nervous system may be just as crucial to worker performance as changes in the optics ofthe eye. Visual processing centers deep within the brain may be involved in these changes, and standard clinical tests are not designed to detect such problems. Glare, for example, has a stronger effect with age, making it more 14
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THE RETINA The lens focuses light on the retina, a tissue thin as an onion skin that lines the inside of the eyeball. Crisscrossed with veins and arteries and containing more than 130 million individual light detectors, the retina is the eye's version of photographic film. The light detectors, special types of nerve cells, convert light into electrical signals that carry information. These signals, traveling about 300 miles per hour, are transmitted to the brain through the optic nerve. The retina actually contains two kinds of light sensors, and both are named for their shape. In the majority are the 120 million rods, which provide only black-and-white vision and are found throughout the retina except at its center. The rods are most adept at detecting dim light. In contrast, 10 million or so cones respond to color and bright light and are concentrated at the center of the retina, known as the fovea. The pinhead-sized fovea, along with the yellowish surrounding area, known as the macula, are the headquarters for the type of vision needed for reading fine print and sewing. This area of the retina often degenerates as people age. Both rods and cones use pigments to initiate the conversion of light into electrical signals. Each cone, for example, contains a pigment that is most sensitive to either blue, green, or red light. Any single light beam will trigger chemical reactions in each of the three types of pigmented cones, creating tiny electrical signals that the brain uses to distinguish among more than 150 hues. Rods, on the other hand, contain only one pigment, rhodopsin, which is bleached by light into two colorless molecules. The bleaching process sets off electrical impulses that are passed to the optic nerve. difficult to see. At the workplace, glare from the screen of a word processing terminal may cause more problems for older people than for their younger colleagues. Since glare can be minimized, awareness ofthe problem may be enough to improve worker efficiency and improve eyesight. Sometimes special methods of training may help older workers perform visual tasks successfully, minimizing the effects of normal aging of the eye. Human factors engineer Sara Czaja at the State University of New York at Buffalo and other researchers have found that older people can be trained to inspect manufactured parts for defects despite ~5
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the visual demands of the task and the limitations of their visual function. But the job "raining methods that worked best with older people differed from traditional techniques. Active, learning-by-doing methods are more effective than methods that require memorization. Some studies have shown that allotting extra training time and giving imme- diate feedback dramatically improve the performance of older workers. These methods of compensating for age-related impairment of vision may also benefit younger employees. Changes in Lighting Older people may have difficulty in adapting to sudden changes in lighting. It may take their eyes a few extra minutes to adjust from a darkened hallway to broad daylight. In the laboratory, older people's eyes took longer to react and adjust to the bright light of a flashbulb. A recent survey in the Chicago area revealed that adapting to bright lights was one of eight eye problems commonly reported by both young and old people. Looking at Life Through Cloudy Glasses One survey took a unique approach to learning about impaired vision: five young architecture students wore specially coated glasses that simulated glare and allowed only one-fourth of available light to reach their eyes. The glasses also reduced eyesight to 20/40 vision. According to the study designer, Leon Pastalan of the University of Michigan, the lenses ofthe glasses scattered light, simulating a condition "that most people will eventually be reduced to if they live long enough- although some might not experience it until their 60s or 70s." Students in the study, who wore the glasses periodically for six months, kept a log of their observations and reactions in three standard settings the home, a shopping center, and a senior citizens' center. Glare from both artificial and natural light was the predominant com- plaint among participants. For instance, the group found that light streaming in on a supermarket window obliterated most of the printing on packages on nearby shelves. Moreover, intense light from a single artificial source created more uncomfortable glare than light from sev- eral less intense sources. The students reported that colors appeared less bright, and were harder to distinguish. Boundaries between light-green walls and blue- green carpets, for example, were virtually impossible to detect. As a result, navigation in a uniformly colored environment would be hazard- ous. Impaired depth perception and decreased sensitivity to color contrast were a double threat for walking down stairs both conditions made it difficult to judge the location of steps, especially if riser and tread were painted similar colors. 16
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To alleviate these problems, which are also common complaints of older people, Pastalan recommended a number of design changes in the workplace. Glare can be reduced by using materials that are poor light reflectors. Signs should be printed in high-contrast colors; white symbols on a dark background are preferable to the more common black-on-white lettering. Printed matter and other visual information should be free of glare and displayed in an easy-to-read location. The use of stairs should be minimized. Reds and yellows should predominate in areas where color accents are needed. Finally, both overhead and desk lighting should gen- erally be increased. Other studies have also found that sensitivity to contrast, which determines one's ability to perceive details of an object or scene, decreases with age. Colors become more difficult to distinguish, driving in the low light of twilight may be hazardous, and picking out individual faces in a crowd may be nearly impossible in dim light. Scientists have found that older persons find it hard to detect objects that are clustered together rather than spread far apart. For example, it may be difficult for an older person to read a large-print book if there is insufficient white space between the black letters. Older people's ability to distinguish between visual events that occur in sequence is sometimes impaired. In laboratory experiments, events that appeared entirely separate to younger observers seemed to the elderly to overlap. Clutter Drive along the main road in County Kerry, Ireland, and you're likely to come screeching to a halt. A typical signpost points left to Black Head, right to Lisdoonvorna, northeast to Ailwee Cave - there is a jungle of arrows pointing in eight different directions, and most people need time to search out the one direction they want. In the same way that a confusing signpost may stump drivers, the barrage of visual information from a cluttered work area may prevent employees from performing a task quickly. Scientists simulate these and other real-life conditions in an effort to bridge the gap between academic research and the workplace. At Northwestern University, researchers tested the ability of young and old volunteers to pick out a cartoon face from a jumble of other images flashed on a television screen. The experiment was conducted in two parts. In the first, volunteers were asked to locate a small cartoon face that appeared for only a tenth of a second on a television screen. Young and old members of the group performed this task equally well, but then things got tougher. The Northwestern researchers, headed by Robert SekuTer, added a series of distracting images to each appear- ance of the cartoon figure. Like the cluttered signpost in County Kerry, the extra images scattered about the screen made it more difficult to 17
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locate the desired figure. Older people averaged twice as many errors as younger people. The researchers took their test a step further. The group of older volunteers was asked to practice the video test, typically repeating it 64 times in 3 days. At the end of the practice sessions, the older group performed as well as the younger one. Sekuler strikes a cautiously opti- mistic note about these results: although the performance of many visual ; DIABETIC RETINOPATHY Among the complications of diabetes is a disorder that damages the blood supply to the retina. Older diabetics, particu- larly those who have had the disease for more than five years, are at risk for diabetic retinopathy. According to a 1978 estimate of the National Society to Prevent Blindness, 40 percent of the nation's 10 million diabetics have at least a mild form of the disorder, and about 3 percent have severe visual impairment. Early stages are marked by deterioration and ballooning of small blood vessels that nourish the eye. Researchers are unsure why the eye's circulatory system weakens in diabetics, but fluid leaking from the vessels is known to collect and settle in the retina. Although blurring of vision may occur if fluid collects in the macula, 80 percent of patients experience no symptoms at this stage. As the disease advances, severe impairment and blindness may result. Lasers can be used to treat leaky blood vessels, preventing additional damage to the retina. In addition, if leaking fluid has clouded the clear eye fluid, known as the vitreous humor, it can be surgically replaced. Because diabetic retinopathy has few, if any, early symptoms, doctors recommend that diabetics receive peri- odic eye checkups. Among the visually impaired workers at one company is Dan N., a 59-year-old drill press operator employed there for 16 years. A supervisor suddenly noticed that Dan had become error- prone and was scrapping an unusually large number of parts. He referred Dan, already under the care of an eye specialist, for an exam. The medical stab diagnosed the problem as diabetic retino- pathy. Dan, who had a reputation as a good worker, would not be eligible for optimum retirement benefits for three more years. The firm kept him on but transferred him to the day shift and changed his job assignment to machine parts finisher. This task did not require the near-perfect vision needed for finely detailed machin- ing, and Dan remained productive until his retirement. 18
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tasks cannot be improved by simple training or repetition alone, practice may help boost the capabilities of older people in the work force. Driving Driving is one area that has been studied extensively outside the laboratory by vision scientists. The visual skills used on the road are similar to those needed in the workplace, and the number of drivers over the age of 65 is rapidly increasing. Elderly drivers have a different profile of accidents and violations than the young. Although older people have few high-speed accidents or major violations, they are prone to mishaps caused by failure to heed signs, give right-of-way, or turn safely. Among a group of drivers in California, researchers recently determined that accident rates were twice as high for people with reduced peripheral (side) vision in both eyes as for the group at large. One important and surprising result of this research was that 60 percent of the people in the study whose vision was impaired were unaware of their problem. Eighty percent of the people in the study with reduced peripheral vision in the study were over age 65; however, only those with impair- ment in both eyes had a higher accident rate. Other tests have shown that cataracts, glaucoma, and retinal disorders are common causes of loss of peripheral vision among drivers. Researchers have discovered in the laboratory that older people have difficulty identifying one shape or symbol, such as a stop sign, when it is surrounded by extraneous symbols. Older individuals appear to be distracted from visual tasks more easily than younger people when presented with competing messages. Although perceptual and visual processing problems of the el- derly are still under intense study, many eye diseases and dysfunctions can readily be identified and treated by eye specialists, especially if caught early. Among these are glaucoma, cataracts, eye complications associated with diabetes, and degeneration of central, or macular, vision. 19
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Representative terms from entire chapter: