Sensory Impairment, Aging

Seeing

Acuity is what most people mean when they talk about seeing ability. Visual acuity is measured with the aid of charts such as the Snellen chart. On a Snellen chart, letters or numbers of varied size are presented with the knowledge of what can be seen by the “normal” eye at a specific distance. For example, if the “normal eye” can see a specified letter at 40 feet but the person tested can see the letter at 20 feet but no further, this is reported as 20/40 vision. Research indicates that with age, there can be as much as a sixfold decline in visual acuity (Gittings & Fozard, 1986). In addition to the decline in visual acuity at distances, there is a loss in ability to focus on objects that are close. This is known as presbyopia and is a part of normal aging. This happens because with age, the lens of the eye becomes more dense and less flexible. As this happens, it does not change shape as easily as before. Because the lens must be most flexible in order to see nearby objects, it cannot accommodate properly, and those objects at close range appear increasingly out of focus. This change in accommodation is gradual, occurring across the life span. Most people, however, come to recognize the problem in a practical sense in their late 30s or early 40s, when they begin to have difficulty reading. The problem may first appear under poor lighting conditions, such as attempting to read a map under a streetlamp or in a car under the dome light.

There is a set of related problems as the lens becomes denser with age. As the lens becomes denser, it also becomes increasingly opaque or clouded. When this happens, less light reaches the retina, and this is one of the reasons why older people see less well in the dark. A second reason for poor vision in the dark is that with age, the pupils of the eyes do not dilate as well as they once did. But the opaque lens also scatters light and creates problems with glare. Many older people consider the problem of glare to be particularly unpleasant. This is one reason why older people prefer darker rooms to thoroughly bright ones. That is, it may be preferable to see less well than to deal with the discomfort of glare. And then finally, as the lens ages and becomes opaque, it becomes gradually more yellow. This creates a filtering effect, with colors of the shorter wavelengths being filtered out, including greens, blues, and violets. This makes perception and discrimination of these colors difficult (Fozard & Gordon-Salant, 2001). Older people may have difficulty reading text printed in these colors. It may also be difficult for older people to differentiate pill capsules that are distributed in these colors.

...