American Medical Association Family Medical Guide - American Medical Association [728]
Farsightedness
In farsightedness, the cornea and lens focus the light rays from nearby objects behind the retina, producing a blurred image. Distant objects are usually seen clearly.
Diagnosis and Treatment
A diagnosis of farsightedness is based on the symptoms, a family health history, an eye examination, and the results of vision tests.
In younger people, mild farsightedness is often overcome by a natural process called accommodation, in which the ciliary body muscles (muscles surrounding the lens that help to control the shape of the lens) contract to thicken the lens and make it more convex. This brings the focal point for nearby objects forward onto the retina and produces a sharp, clear image. Farsighted people whose eyes can accommodate well usually do not need treatment.
To correct farsightedness, a doctor will prescribe glasses or contact lenses to boost the focusing power of the cornea and lens and move the focal point forward onto the retina to enable you to see more clearly. As you get older, usually beginning after age 40, the ciliary body muscles in the eye may gradually weaken. For this reason, you will probably need stronger glasses every few years. In some cases, ophthalmologists may recommend LASIK (see page 1030) to correct farsightedness.
Presbyopia
At rest, the lens in the normal eye is focused for distance vision. To focus on closer objects, the ciliary body muscles in the eye contract to thicken the lens and make it more convex (curved outward), a natural process called accommodation. With age, the lens of the eye hardens, gradually reducing its ability to accommodate (focus on nearby objects). This condition, called presbyopia, usually develops when a person is in his or her mid-40s, and gradually worsens as he or she gets older.
Symptoms
In presbyopia, a person can focus on nearby objects only by holding them at a distance. For example, to read, the person may need to hold a book or newspaper at arm’s length from his or her eyes. If you find that close objects are slightly blurred unless you hold them away from you, see an ophthalmologist (eye MD) for a thorough eye examination (see page 1028).
Diagnosis and Treatment
A diagnosis of presbyopia is based on the symptoms, an eye examination, and the results of vision tests.
To correct presbyopia, your doctor will prescribe glasses to compensate for the inability of the lens to focus, which will enable you to see nearby objects clearly. You will need slightly stronger glasses every few years as you get older, until about age 65, to compensate for your decreasing focusing ability. After age 65, the lenses of the eyes stop changing.
If you are already wearing glasses to correct a focusing disorder, you can avoid the need for two pairs of glasses by getting bifocals. In bifocals, the upper part of each lens is for distance vision and the lower part is for close vision. Some types of bifocals gradually change strength from the middle of the lens to the bottom without a visible line between the lenses. Bifocal contact lenses are also available, or you may want to consider wearing a contact lens focused for distance vision in one eye and a contact lens focused for close vision in the other eye (called monovision).
Astigmatism
Astigmatism is distorted vision caused by an uneven curvature of the front surface of the cornea (the clear, protective covering at the front of the eye). This uneven shape prevents light from focusing properly on the retina.
Symptoms
Although mild astigmatism usually does not produce noticeable symptoms, more severe astigmatism may cause a person to see vertical, horizontal, or diagonal lines out of focus. Astigmatism commonly occurs along with farsightedness (see previous page) or nearsightedness (see page 1030), but in some people with astigmatism, vision may be blurred at all distances. If you