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GENERAL PRINCIPLES

Vision impairment is relatively rare in people younger than 65 years of age, but its incidence steadily increases to almost 24% of those 80 years and older. Not surprisingly, vision impairment can have a significant impact on a patient’s quality of life. It is associated with social isolation, anxiety, depression, and a loss of independence. It can affect balance, leading to more frequent falls, and has been shown to negatively affect physical activity.

The following three levels are used to categorize the severity of vision loss*:

  1. Normal vision: Visual acuity ≥20/40

  2. Visual impairment: Visual acuity <20/40 but <20/200

  3. Legal blindness: Acuity ≤20/200 in the better eye, or total visual field <20 degrees

*It is assumed the patient is wearing the best glasses (or contact lens) correction.

NORMAL CHANGES IN THE AGING EYE

Clinical Findings

Although not meeting the definition of vision impairment, there are still a number of changes in the aging eye leading to diminished vision. Changes in refractive error in older adults may cause reduced vision. In all adults, the crystalline lens gradually becomes less flexible and less able to change its curvature (accommodate) with age. This results in the condition known as presbyopia, in which patients lose the ability to focus their eyes on near objects. Contrast sensitivity is the ability to distinguish objects from the background when they are similar in brightness, and this ability decreases slightly with age. A real-life example of contrast sensitivity is the ability to see a curb when the sidewalk is similar in color and brightness. In eyes with no significant pathology, the loss of contrast sensitivity with aging exists but is not significant enough to cause problems seeing curbs in well-lit conditions. Notably, the ability to see well in dim light also becomes diminished in older adults. When combined with reduced contrast sensitivity, this reduced sensitivity in dim illumination may explain why older drivers may have difficulty seeing pedestrians at night. Both the change in contrast sensitivity and the reduced ability to see in dim illumination result from a combination of decreases in pupil size and progressive increases in the light absorption of the lens. This age-related reduction in retinal illumination is substantial. A typical 60-year-old’s retina receives only about one-third of the light that a typical 20-year-old receives. As a result of the tendency for opacities to form in the aging lens and cornea, older adults are increasingly sensitive to glare caused by scattered light in the eye. In addition, largely due to neural changes in the retina, there is an age-related reduction in the ability to adapt to sudden changes in illumination. Finally, dry eye, especially in older women, is also common. Symptoms include a mild foreign-body sensation, burning, small fluctuations in vision, and even (reflexive) tearing because of mild corneal ...

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