Effects of Aging

In middle age, the lens of the eye becomes less flexible and less able to thicken, and thus less able to focus on nearby objects, a condition called presbyopia. Reading glasses, or bifocal lenses, can help compensate for this problem.

In old age, changes to the sclera (the white of the eyes) include yellowing or browning due to many years of exposure to ultraviolet light, wind, and dust; random splotches of pigment (more common in people with a dark complexion); and a bluish hue due to thinning of the sclera.

The number of mucous cells in the conjunctiva may decrease with age. Tear production may also decrease with age, so that fewer tears are available to keep the surface of the eye moist. Both of these changes explain why older people are more likely to have dry eyes.

Arcus senilis (a deposit of calcium and cholesterol salts) appears as a gray-white ring at the edge of the cornea. It is common in people older than 60. Arcus senilis does not affect vision.

Some diseases of the retina (see Section 20, Chapter 234) are more likely to occur in old age, including macular degeneration, diabetic retinopathy, and retinal detachment. Other eye diseases, such as cataracts and dry eye, become common.

The muscles that squeeze the eyelids shut decrease in strength with age; this, combined with age-related looseness of the eyelids, sometimes results in the lower eyelid falling away from the eyeball, a condition called ectropion. In some older people the fat around the orbit shrinks, causing the eyeball to sink into the orbit.

The muscles that work to regulate the size of the pupils weaken with age. The pupils become smaller, react more sluggishly to light, and dilate more slowly in the dark. Therefore, people older than 60 may find that objects are not as bright, that they are dazzled initially when going outdoors (or when facing oncoming cars during night driving), and that they have difficulty going from a brightly lit environment to a darker one. These changes may be particularly bothersome when combined with the effects of a cataract.

Other changes in eye function also occur as people age. The sharpness of vision (acuity) is reduced despite the use of the best glasses. The amount of light that reaches the back of the retina is reduced, increasing the need for brighter illumination and for greater contrast between objects and the background. Color perception and depth perception are reduced. Older people may also see increased numbers of floating black spots (floaters). Floaters do not significantly interfere with vision.