Common Visual Problems: Symptoms and Treatment, Part I

Fri, 9/5/08 - 4:54pm
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Author(s):

Paul E. Michelson, MD, FACS

THE CHALLENGE

In the year 2000, nearly one million Americans over age 40 years were deemed “blind,” and 2.4 million had “low vision.” The incidence of both blindness and low vision in Americans is projected to increase dramatically by the year 2020. Persons over age 80 years accounted for more than two-thirds of the observed blindness, and, as we know, this more elderly group is the fastest-growing segment of the U.S. population.1

In a 2-year study of individuals age 65-84 years, 25% suffered “significant vision loss” over that interval (visual acuity diminished in 25%; contrast sensitivity and visual field loss occurred in 10%). In a cohort of individuals over age 85 years, one-half had better than 20/40 acuity, but with low contrast and “veiling glare,” 75% had their acuity diminished to less than 20/200; 50% of these individuals had no stereopsis. “Glare recovery” took longer than 2 minutes versus 15 seconds for those under age 65 years, and visual fields tested with “divided attention” (ie, a central distracting task) is about one-half the expanse of that for individuals younger than age 65 years.2 In addition, this loss of visual function is often compounded by other age-related disabilities. Of special note is the fact that high-contrast visual acuity, the most commonly used measure of visual function, is the slowest and probably the least sensitive measure of visual function to decline with age.3-5

Poor visual function has deleterious effects on vocation and avocations, driving ability (especially at night), and routine activities of daily living. Positive correlations have been documented between vision loss and auto accidents, loss of employment, increasing dependence on others, social isolation, depression, personal accidents, hip fractures, and ultimately, mortality.6-12

THE NATURE OF “VISION”

Obviously, from the foregoing discussion, vision and visual functioning is more than a simple measure of central, high-contrast acuity. Central visual acuity, as measured on the common eye charts, is certainly a critical aspect of overall visual functioning. But it is actually more important for our activities of daily living to have an adequate visual field—the panorama through which we are able to see—than it is to have central keen acuity. While our central acuity allows us to perform fine-detailed tasks, such as reading and identifying small objects at a distance, the visual field is critical for our orientation and mobility. Thus, individuals with significantly impaired visual fields are far more disabled visually than those with dramatically reduced central acuity. They cannot navigate and get about without assistance8 (Figures 1A and 1B). Binocularity and stereopsis represent other parameters of overall visual function, which are critical if we are to recognize our position in space, and the relative positions and distances of other people and objects in our environment.

Contrast sensitivity is the term applied to the quality of our vision that allows us to detect contours, shades of gray-on-gray, and various saturations of color. Contrast sensitivity is probably the best present means of assessing overall visual function, as it most closely represents the world as we see it—in shades of grays and colors, rather than in high-contrast black-and-white. Contrast sensitivity declines “normally” with aging, dramatically moreso in certain eye diseases (Figure 2).

References:

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