Normal changes in vision occur with age, as do abnormal changes caused by age-related eye disorders. One in six Americans (13.5 million people) 45 years of age and older report some problem with their vision, and more than one in four of those age 75 and older report a vision problem (The Lighthouse Research Institute, 1995). While medical and surgical interventions can eliminate or reduce vision loss due to some eye disorders, for many older people, vision rehabilitation is the key to maintaining independence. This article will address normal age-related changes in vision, age-related eye disorders-which are not normal-and the risk factors and interventions and treatments associated with eye disorders. It presents practical information about the vision rehabilitation service network, rehabilitation specialists, and ways to gain access to the valuable expertise available. The Appendix provides a questionnaire for screening functional vision.
NORMAL AGE-RELATED CHANGES IN VISION
Everyone can expect to experience common age-related changes in vision. A number of basic interventions and environmental changes can ameliorate their impact.
At about age 40 to 50, the most common age-related vision change, presbyopia, occurs. The lens of the eye becomes denser, more yellow, and less elastic, with the result that it is harder to focus for near tasks such as reading. Presbyopia is correctable with reading glasses or glasses with bifocal, trifocal, or progressive lenses. The cornea generally remains clear, but it may become slightly thicker and thus more likely to scatter light. These changes account for the loss of accommodation (focusing power).
Visual acuity is remarkably well preserved in the aging eye, as the Framingham Heart Study (Kannel and Gordon, 1973), based upon an evaluation of an entire town, documented. Some 92 percent of the individuals in the town between ages 65 and 74 and 70 percent between ages 75 and 85 retained corrected visual acuity of at least 20/25 in the better eye. However, it is important to understand that visual function is dependent on much more than just visual acuity.
The pupil of the eye tends to become smaller with age, permitting less light to enter the eye. On average, older people need more light than younger people do. This need increases approximately 10 percent per decade. When lighting is optimal for the older adult, normal vision is quite good. However, many older adults experience difficulty performing visual tasks under adverse lighting or changing illumination levels. Most older individuals adjust more slowly to changes in illumination and are generally able to see less at night than their younger counterparts.
Generally, older adults have some loss of contrast sensitivity, meaning that they need sharper contrasts in order to discriminate between objects-for example, they might have a hard time seeing the edge between one step and another. Colors also tend to be less vivid and appear faded as people age. These difficulties are often made worse by increased sensitivity to glare. The thickened cornea or yellowing lens scatters light and interferes with vision. Older adults are more susceptible to visual discomfort under bright light conditions or at night-they often have trouble with oncoming headlights, for example.
AGE-RELATED VISION DISORDERS
The World Health Organization in its ninth revision of the International Classification of Diseases officially abandoned the simple dichotomy of vision versus blindness. This change recognizes the vast continuum that exists between normal vision and blindness and includes the area of "low vision" (Colenbrander and Fletcher, 1995). There are indeed those who experience total blindness, but the majority (more than 90 percent) of adults experiencing vision decline in later life do not lose all usable sight. Older adults constitute the most vulnerable group for common eye disorders such as cataract, macular degeneration, glaucoma, and diabetic retinopathy. …