Normal Age-Related Vision Changes and Their Effects on Vision
By Michael F. Marmor, MD
It is debatable whether any decline in visual function with age is truly "normal," or whether deterioration related to aging is strictly necessary. However, it is still important to distinguish between a quality of vision that we accept as an accompaniment of good health and that which we call pathologic because it impairs ordinary levels of function. Definite changes occur in vision with age, but, in general, excellent visual function among older adults is the rule rather than the exception. Poor vision among older adults should be evaluated, and never just passed off as a function of age.
Visual Acuity
The Framingham Heart Study, based upon prospective examination of an entire town, showed that visual acuity is remarkably well preserved in the elderly population. Corrected visual acuity of at least 20/25 in the better eye is retained by 98 percent of individuals between ages 52 and 64, 92 percent between 65 and 74, and 70 percent between 75 and 85. Thus, we should not expect poor acuity in older adults. At the same time, these data show that more than 10 percent of the population over 75 has acuity poor enough to affect driving and other daily tasks. A significant minority of elderly patients has pathological visual impairment that must be recognized to ensure they receive medical treatment and advice on managing their disability.
The causes of diminished visual acuity with age are not entirely clear. A good part of the loss undoubtedly results from changes in the lens due to aging, narrowing of the pupil and the gradual loss of visual neurons. The fact that a few elderly individuals retain exceptionally sharp acuity provides hope that the aging process might eventually be moderated.
Accommodation
Perhaps the most universal age-related ocular deficiency is presbyopia, or the loss of accommodation (focusing power). A young child can hold print practically up to the nose, but somewhere between ages 45 and 50, individuals corrected for distance vision will start holding the newspaper at arm's length. By roughly age 60, accommodation stabilizes, and virtually everyone must wear different glasses or bifocals for reading and for distance. Note that presbyopia is solely a matter of focusing power; it has nothing to do with basic nearsightedness or farsightedness.
Presbyopia is mostly a nuisance, since optical correction is easily available as bifocals, trifocals, reading glasses or continuous range glasses. It may, however, cause difficulty in certain situations. For example, bifocal wearers have difficulty walking down stairs since they cannot see their feet through the reading segment. Bifocals are also ill suited for intermediate distance tasks, such as playing music or using a computer. Special glasses for intermediate range may be worth the cost to facilitate these activities.
Night and Color Vision
Most older adults adjust more slowly to changes in illumination and have greater difficulty seeing in dim light. Blue color may appear dark and hard to distinguish from green, presumably because the yellowish elderly lens absorbs blue light selectively. After cataract surgery, most patients notice a brightening of colors at the blue end of the spectrum.
Contrast and Glare Sensitivity
Visual acuity is important for reading, but the recognition of objects and faces in the real world requires the recognition of contrasts, textures and patterns. Most of the cells in our retina and brain are coded to recognize edges and contrast, rather than absolute light or darkness. Thus, our ability to discriminate light from dark is central to the process of perception. Much of the loss of contrast sensitivity probably relates to the reduction of light through the smaller pupil and the increased density or haziness of the older lens. The net effect is that it is harder to recognize faces and objects, especially at dusk or in dim lighting where contrast is poor.
These difficulties are exacerbated by increased sensitivity to glare. Since even minimal haze in the cornea or lens will scatter light and interfere with vision, older adults often experience discomfort and, sometimes, even disability under bright outdoor conditions.
Visual Quality and Illumination
Adverse lighting or changing illumination makes vision more difficult; subtle contrasts or colors might be difficult to discriminate. Harsh or "cold" fluorescent lighting may cause glare and discomfort. In contrast, indirect and warm (incandescent) lighting is apt to be more comfortable. Paradoxically, older individuals need more light to see, and are also more sensitive to glare.
The quality of vision is a valid and important parameter for daily life. If complaints about vision are taken seriously, many of the problems can be minimized with knowledgeable advice from eye care specialists and common sense.
Examples of Anatomic Age-Related Vision Changes
Many of the visual effects of age are a direct result of anatomical changes that characterize the older eye.
Cornea -- Generally remains clear. However, as some of the endothelial cells (which maintain clarity) drop out, the cornea may become more likely to scatter light.
Lens -- Invariably becomes denser, more yellow and less elastic, accounting for subtle visual changes as well as the loss of accommodation.
Pupil --Becomes smaller, admitting less light to the eye. Decreased capacity to adjust to changing levels of illumination.
Vitreous gel -- Tends to condense and collapse. Bits of dense gel may appear as floaters against the sky or a white wall.
Retina -- Embryonically a part of the brain (which loses cells). The number of nerve cells within the retina and visual cortex gradually reduces over time.
Retinal vasculature -- Ages along with vasculature throughout the body.
Michael F. Marmor, MD, is a Professor, Department of Ophthalmology, Stanford University, Stanford, CA.
Source: The Lighthouse Inc.'s Aging & Vision News newsletter (Spring 1998 issue)
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