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. For more information on the effects of age on the eye, see Changes in the Body With Aging: Eyes.
In old age, changes to the eye include the following:
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. However, even though the eyes tend to be dry normally, tearing can be significant when the eyes are irritated, such as when an onion is cut or an object contacts the eye.
Arcus senilis (a deposit of calcium and cholesterol salts) appears as a gray-white ring at the edge of the cornea. It is common among people older than 60. Arcus senilis does not affect vision.
Some diseases of the retina are more likely to occur in old age, including macular degeneration, diabetic retinopathy (if people have diabetes), and detachment of the retina. Other eye diseases, such as cataracts, also become common.
The muscles that squeeze the eyelids shut decrease in strength with age. This decrease in strength, combined with gravity and age-related looseness of the eyelids, sometimes causes the lower eyelid to turn outward from the eyeball. This condition is called ectropion. Sometimes, because of age-related looseness affecting a different part of the eyelid, the lower eyelid turns inward, causing the eyelashes to rub against the eyeball. This condition is called entropion. When the upper eyelid is affected, the lid can droop, a condition called ptosis.
In some older people, the fat around the orbit shrinks, causing the eyeball to sink backward into the orbit. This condition is called enophthalmos. Because of lax tissues in the eyelids, the orbital fat can also bulge forward into the eyelids, making them appear constantly puffy. Enophthalmos, if significant, may cause a slight blockage of a person's peripheral (side) vision.
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 appear dimmer, 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 use of the best glasses, especially in people who have a cataract, macular degeneration, or advanced glaucoma (see table Some Disorders That Affect Mainly Older People). 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. Older people may also see increased numbers of floating black spots (floaters). Floaters usually do not significantly interfere with vision.