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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:
visual processing
