DEAR DR. DONOHUE: What is a cataract? My mother, 83, just had one removed. My brother, 64, had cataracts removed from both eyes. Are they hereditary? What are my chances of getting one? I read a lot. – C.B.

ANSWER: Less than a fingertip inward from the pupil is the eye lens, about the size and shape of a small olive pit. Unlike an olive pit, it is clear. It focuses incoming light onto the retina so people get a clear image of what they see.

A cataract is a smudge that develops on the lens, like a thumbprint on a window. Aging is the greatest contributor to cataract formation. If doctors looked into the eyes of all people between the ages of 50 and 65, they would find a cataract or the beginnings of one in half of those people’s eyes.

If they examined the eyes of people over 75, they would find a cataract in most of their eyes.

Just about everyone, therefore, has inherited a tendency to develop one. Diabetes, smoking and sunlight exposure contribute to cataract formation.

Wearing sunglasses that block ultraviolet light is one way of minimizing the risk for cataracts from sun exposure. Reading has nothing to do with them.

Even though cataracts are nearly everyone’s fate, not everyone needs to have a clouded lens removed. It’s the patient who determines when and if surgery is needed. Cataracts can blur vision and cause a glare around objects that makes them look like they have a halo. If people with cataracts can carry on their normal activities, then nothing need be done about their cataracts. Cataracts often enlarge at a glacial pace, but when they make it difficult to read, to drive or to perform any of the activities of daily life, then the cloudy lens should be removed. Cataract surgery is one of medicine’s greatest achievements.

The opaque lens is removed, and a new, artificial one replaces it. Gone are the days of thick glasses that used to be worn after cataract surgery, and gone are the days when a person had to lie immobile following surgery.

Today, it is most often done as outpatient surgery.

DEAR DR. DONOHUE: Our adult daughter was diagnosed with tuberculosis. The doctor said that two weeks after medication began she would not be contagious. Our PPD skin tests and chest X-rays are normal. Is it necessary to have a second round of tests before visiting our pregnant daughter-in-law? How much time should pass between the tests? The baby will be born in five months. Can we make the trip to see it? – J.P.

ANSWER: A person with TB transmits the TB germ in droplets when he or she coughs or sneezes. Heavily infected people can transmit germs while talking if they are in a small room where air circulation is poor.

Although one TB germ is enough to start an infection, infections usually come from prolonged exposure to many airborne droplets containing the germ.

Your doctor is correct. As a rule, after two weeks of treatment, a patient is no longer considered to be a source of infection.

People exposed to an infected patient are skin-tested as soon as possible after the exposure. If the skin test is negative, they are asked to return for a repeat skin test in eight weeks. That allows enough time to pass for the skin test to turn positive if they have inhaled a TB germ.

Actually, after inhaling a germ, the skin test almost always becomes positive in two to four weeks. The eight-week rule was established to assure that there will be no falsely negative skin tests. You have plenty of time to take care of these matters before you visit your daughter-in-law.

DEAR DR. DONOHUE: My niece and her husband have been trying a long time to have a baby. They are in their middle 30s. We think that the problem might be his drinking. He drinks a six- to 12-pack of beer every night. Could alcohol be the reason? My niece’s biological clock is ticking. – L.A.

ANSWER: On the list of causes for male infertility, you will find heavy alcohol drinking. Alcohol in excess can depress the sperm count. Your niece’s husband fits the definition of heavy drinking.

Dr. Donohue regrets that he is unable to answer individual letters, but he will incorporate them in his column whenever possible. Readers may write him or request an order form of available health newsletters at P.O. Box 536475, Orlando, FL 32853-6475.