Age-Related Changes in Ocular Function

Age-related changes in the eye contribute to functional differences in accommodation, visual acuity, contrast sensitivity, color vision, light adaptation, and visual field size and may lead to symptoms of glare, flashing lights, and floaters.

Accommodation: When viewing an object closer than 2 feet, the ciliary muscles contract, allowing the lens to change shape (accommodate) to provide additional refractive power to focus the near object on the retina; the pupil also constricts. With aging, the lens becomes denser and less elastic, and the ability to accommodate to near vision is lessened (presbyopia). Presbyopia is a universal age-related change in vision beginning in a person's 40s, is one of the most noticeable physiologic changes of aging, and is corrected with reading glasses, bifocal glasses, or contact lenses. Because loss of accommodation is progressive between a person's 40s and 60s, reading lenses usually must be changed every 2 or 3 yr.

Visual acuity: Uncorrected visual acuity may begin to decrease in a normal healthy person around age 50. Optically, the eye becomes more hyperopic (farsighted; the point of focus falls behind the retina because the cornea is too flatly curved or the axial length is too short) and astigmatic (nonspherical curvature of the cornea or lens causes light rays to focus at different points) with aging. Subtle neurologic changes in brain functioning can cause visual acuity involving fast-moving objects to decline, resulting in the perception of decreased visual acuity. "Normal 20/20 vision" may not be obtainable in the very old.

Contrast sensitivity: The ability to distinguish extremely fine details (eg, mesh size in a window screen) decreases with aging. Cause is unclear, but it may be due to a decrease in the actual number of neurons in the visual pathway. This decline in contrast sensitivity may contribute to a decline in the ability of the elderly to enjoy fine, detailed activities (eg, quilting) even though vision is "normal."

Glare: Elderly patients often complain of decreased visual perception resulting from glare even though measured visual acuity is normal. Glare is caused by opacities in the lens and vitreous humor that develop with aging and that increase the scattering of light in the ocular media. Opacities can be observed using an ophthalmoscope set to +10 diopters (for lens opacities) and +2 diopters (for vitreous opacities).

Opacities in the lens may be stable for many years, causing symptoms but without reducing visual acuity. Lens opacities are not generally considered cataracts until visual acuity decreases to 20/30 or worse. As with cataracts, the effect of lens opacities varies by site. Opacities in the cortex (periphery) of the lens are often spokelike and cause glare especially at night or in dim light when the pupil is slightly dilated; a typical symptom is glare with oncoming headlights while driving at night. These opacities usually have little effect on visual acuity.

Nuclear (central part of the lens) opacities cause glare but also have little effect on visual acuity; early on, they may actually improve close vision in the elderly, a phenomenon known as second sight. This improvement in close vision occurs because when the nuclear opacity is still highly transparent, it increases the refractive index of the lens, making the lens magnify the close field of view. This increased refractive ability of the lens can partially compensate for the loss of accommodation (presbyopia) and enable people who have been using glasses for reading to read again without glasses. However, as the opacity becomes denser, it decreases the amount of light reaching the retina and interferes with sight. At this point, people cannot read, even with glasses.

Posterior subcapsular opacities (in the central cortex region just beneath the posterior lens capsule) are closer to the focal point of the lens through which all light must pass on the way to the retina. As a result, they tend to scatter light to a greater extent, especially in bright light and in people with small pupils. Sunglasses help reduce glare.

Flashing lights: Flashing lights are caused by age-related changes in the vitreous humor. As the eye ages, the vitreous becomes more liquefied, and the vitreous cortex, (which holds the vitreous humor in place against the retina), thins. These changes often result in shrinkage of the vitreous away from the retina. However, because the vitreous is firmly attached to the retina, the retina is tugged on by collagen fibrils as the vitreous falls away. This tugging triggers electrochemical impulses that are perceived by the brain as flashes of light. The flashes typically occur in one eye at a time, and if they are not accompanied by decreased vision or other changes in visual function, they usually need no further evaluation because the tugging is weak and localized and damage to the retina is unlikely to have occurred. However, if the flashes persist or the perception develops that a veil has descended over the eye or that visual fields are decreased, the patient should be referred immediately for an ophthalmologic examination to exclude retinal detachment.

Floaters: Many patients in their late 50s and early 60s may develop lines, spots, or clusters of dots that move slowly across the field of vision (floaters). Usually, they move more rapidly with eye movements and tend to become stationary when the eye is not moving. Floaters represent aggregates of vitreous humor that have formed within the vitreous cavity. Although floaters are annoying, they usually have no clinical importance. If an ophthalmoscopic examination shows no retinal detachment, the patient should be reassured and encouraged to ignore the floaters, which can gradually become less noticeable. However, a shower of opacities, often accompanied by flashing lights in the peripheral visual field, requires a prompt referral to rule out retinal detachment.

Color vision: Color discrimination declines with aging. Three classes of cones (short wavelength [blue], medium wavelength [green], and long wavelength [red]) are responsible for normal color vision. With aging, all 3 classes decline in sensitivity. Colors appear to be less bright, and contrasts between colors are less noticeable to the elderly person than to a younger caregiver, sometimes resulting in different perceptions of color combinations in clothing.

In addition, the lens becomes yellow with aging, thus reducing transparency for short wavelengths more than for medium and long wavelengths. In people > 60 yr, this age-related change results in a reduction in discrimination of blue objects, which often appear gray; blue print and blue background typically appear washed out. This condition can be confirmed with the use of color plates during a routine eye examination. People who use color discrimination in their professions (eg, artists, seamstresses, electricians) need to be alert to these changes.

Light adaptation: All elderly people note that their ability to function safely in poorly lit environments is reduced. With aging, adaptation to darkness and light occurs more slowly, mostly due to age-related changes in iris muscle function and pupil size and to development of non-cataract lens opacities. In transitions from light to dark environments, slower papillary dilation means less light reaches the retina, delaying or reducing adjustment; this can be briefly dangerous such as when an older person enters a movie theater or drives into a dark place, such as a tunnel. Conversely, the pupil is slow to constrict when moving from a dark to a light environment, and the elderly are more likely to be dazzled by glare and reflections when moving from a dark environment to a bright one. Accordingly, it is important to educate the elderly to be cautious in low light environments they cannot illuminate. In addition, safety and comfort would be enhanced by better illumination in places where older adults commonly go (eg, recreational sites, shopping malls, grocery stores, parking lots, stairways in all public buildings, nursing homes, assisted living facilities). Counseling elderly people to increase illumination at home will produce the same benefit--a safer home.

For the same reasons, the amount of ambient light needed for reading by people in their 60s is 3 times that needed by those in their 20s. Increasing the amount of ambient light, for example by increasing the wattage of light bulbs in the home, effectively improves the pleasure and productivity of reading.

Visual field: The size of a normal visual field decreases by about 1° to 3° per decade, so that people in their 70s or 80s may have a total visual field loss of 20° to 30°. This reduction is implicated as a major cause of automobile accidents involving elderly drivers. These age-related changes in peripheral vision must be distinguished by the ophthalmologist from the pathologic ones caused by glaucoma, which tend to occur in specific localized areas of the peripheral visual field.

This topic was last updated May 2005.