Lighting and the Aging Eye
By Robert Rosenberg, OD
Normal vision consists of the accomplishment of several visual skills, and these skills evolve from birth. The visual acuity of a newborn (the ability to discriminate fine details) is not as good as it will be when the infant is a few weeks old. Young children have the ability to accommodate (focus the eyes for close objects) for very close distances, but this decreases gradually from childhood into adolescence and adulthood until it is usually insufficient for normal reading at about age forty. Color discrimination (the ability to match colors that are very nearly the same, but not quite) peaks at about age 25. Contrast sensitivity (the ability to discriminate borders between light and dark) and dark and light. Adaptation (the ability to enter areas of different brightness and immediately be able to see adequately) also diminish as we age.
Although many of these deficiencies can be dealt with through appropriate professional vision care and treatment by an optometrist or ophthalmologist, simply controlling the visual environment can make a considerable difference. Attention to lighting and ergonomic factors, both indoors and out, can help eliminate glare, which causes discomfort and disability.
Glare may be defined as the presence of light in the eye that is not helpful in forming the retinal images of objects in space. Glare of the discomfort type occurs when there are bright lights within our visual field that do not actually obscure objects of interest. Glare of disability variety (sometimes called veiling glare) is exemplified by sunlight striking a dusty window when we attempt to look out; the sun reduces the apparent contrast of the scene by obscuring or veiling visual details. Similarly, reflections from a glossy surface of a book partially obscure or veil the print. In addition to these external sources of glare, older adults are likely to have some internal sources of glare as well. The early changes of the crystalline lens, or early cataract formation, typically cause scattering of light within the eye and results in a veiling glare (or luminance) even in ordinarily favorable environments. What, then, can be done environmentally to enhance visual performance and comfort for the older adult? In the indoor environment, the following steps should be taken:
- Extremes of lighting contrast should be avoided. There should be
only one light source in a work area (much as the sun is our single
light source out-of-doors), and moderate reflectances of walls, floors,
and ceilings should be provided.
- The light source(s) should be placed as far as possible from the usual line of sight so as to be outside the visual field.
- The strongest light should be directly on the task, but the
area a little farther away from the task should also be well lighted at
one third to one fifth of the brightness of the task area. Lighting in
the rest of the area may be even less, but at least one tenth to one
fifteenth as bright.
- The '"luminous ceiling" type of lighting should be
discouraged. With that type of lighting, one can never quite get the
light source out of the visual field short of working while lying on
one's stomach. In an environment with many overhead light sources,
wearing a visor is helpful in reducing overhead sources of glare.
- Desks and other furniture and video terminals (or television
screens) should be properly placed so that bright direct or reflected
light sources are out of the visual field. During daylight hours,
actions as simple as drawing drapes or blinds may be effective.
Approved anti-glare filters are useful to prevent reflections on the
face of the video tube.
- Watching television in the dark should be discouraged. The general rules for visual task comfort should be followed.
Recommendations for controlling light outdoors include:
- Wearing a hat with a wide brim or peak, which can significantly
improve vision and visual comfort by shielding the eyes from glaring
sky light.
- In winter and summer, it's important to wear appropriate sunglasses when outdoors during daylight hours. Indeed, even without snow, glare from the sky and ground is likely to be worse in winter because there are neither leaves on trees to shade the sky nor grass to absorb ground glare.
Finally, it must be noted that proper lighting is just one approach to dealing with changes in vision. Regular vision examinations by an ophthalmologist or optometrist, as well as the employment of special optical devices, help the older adult achieve maximum of his or her sight.
Robert Rosenberg, OD, is a Clinical Consultant, Lighthouse Low Vision Services, and Professor of Optometry, SUNY College of Optometry, New York, NY.
Source: The Lighthouse. Inc Aging & Vision News newsletter (Winter/Spring 1994 issue)
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