DEAR DR. DONOHUE: My son’s kindergarten teacher called me to say she thinks he is colorblind. She says he has a hard time distinguishing the right crayon to use for the color that she tells the kids to choose. Neither his father nor I ever picked up on this. He knows the color words, and I thought he knew what they meant. Maybe he doesn’t.

How do we follow up on this?

If he is colorblind, did he get it from his father? I have been led to believe it happens only to men. His father can discern all colors. I know that for a fact. – N.N.

ANSWER: Let me simplify the colorblind story so that both readers and I can keep it straight.

The most common kind of colorblindness is red-green colorblindness. Affected people cannot discern those two colors. It’s an inherited condition. The defect lies on the X chromosome. Females have two X chromosomes. Males have only one. Their other chromosome is a Y chromosome.

Around 8 percent of men are red-green colorblind. Fewer than 0.5 percent of women are. Few women have this disorder because their second X chromosome is able to override the misinformation on their other X chromosome. Since men have only one X chromosome, the bad information on it is always expressed. Women are carriers; men have the defect.

If your son is colorblind, he inherited it from you. You are the carrier. You have no symptoms, but you do have the colorblind gene on one of your X chromosomes. Half the sons of carrier women develop colorblindness.

Your son should be checked by an eye doctor. The common test for detection of colorblindness is the Ishihara test. It consists of a series of circles filled with colored dots. In the central part of the circles are other colored dots that form numbers. Colorblind people can’t see the numbers.

Paul Newman was said to be colorblind. He and I were not close personal friends, so I can’t say for sure if this is true.

DEAR DR. DONOHUE: I am scheduled for a vasectomy. Have you ever heard that a vasectomy protects a man from prostate cancer? I have heard this. Supposedly a vasectomy prevents sperm from penetrating the prostate gland, which causes cancer. – F.L.

ANSWER: I have heard that. It’s not true. Furthermore, sperm don’t penetrate the prostate gland. If they did, they wouldn’t cause cancer.

I also have heard that a vasectomy leads to heart disease. It doesn’t.

Myths about vasectomies abound.

DEAR DR. DONOHUE: Please tell me about granuloma annulare. My doctor says I have it. I asked what it means, and he said he means a red ring. I could see that for myself.

It doesn’t itch or hurt, but it looks funny. Should I be taking anything for it? – R.K.

ANSWER: “Annulare” (ann-you-LAR-ay) is “ring-shaped.” “Granuloma” is a misnomer for the condition, so let’s skip it.

Granuloma annulare is a very common skin condition, affecting all ages, including infants. It also affects all races. It usually appears on the back of the hands or fingers, at the elbows, at the ankles or on the top of the feet. Most often, it doesn’t cause any symptoms. Its cause isn’t known.

Patience is the best treatment. It often disappears in two years. Sometimes granuloma annulare consists of tens to hundreds of such rings. This kind of involvement takes longer to cure. Applying cortisone ointment to the ring or injecting it with cortisone can hasten its disappearance.

DEAR DR. DONOHUE: A commercial I saw on TV had a grandparent and grandchild talking about peripheral artery disease. It got me wondering if I have it. I got the idea that many older people do. I am 78. What are its signs? – K.M.

ANSWER: Peripheral artery disease, PAD, also goes by the name peripheral vascular disease. It is a common condition in older people, but not every senior citizen has it. Close to 15 percent of those over 70 do.

Here “peripheral” refers to the legs. “Artery disease” is artery clogging, the same process that goes on in heart arteries and culminates in a heart attack. High blood cholesterol, blood fats, blood protein and platelets aggregate on an artery wall and, as the buildup grows, it blocks circulation to the tissues fed by that artery.

Blood doesn’t reach leg muscles in a sufficient amount to support those muscles when they’re active. The common sign of PAD is calf pain while walking. The pain leaves when the person stops walking. Many people with PAD can tell, almost to the inch, when the pain will begin. The pain indicates leg muscles aren’t getting enough blood.

A simple office test to detect PAD is to compare blood pressure taken at the ankles with blood pressure taken in the arms. The two readings should be close. With PAD, the ankle blood pressure is lower than arm pressure due to the obstruction to blood flow.

Management of PAD is similar to management of clogged heart arteries. Blood cholesterol has to be lowered, blood pressure normalized and blood sugar controlled. Weight reduction, if indicated, is important and daily exercise, – even though pain occurs during walking – has to become routine. Cigarette smoking, of course, is out of the question.

If the doctor does confirm a diagnosis of PAD, prescription medicines help blood get around artery blockages.

Aspirin, Plavix and Pletal are examples of such medicines. When the obstruction is sizable, then leg arteries can undergo the same kinds of treatments as heart arteries – bypass surgery or stents.

The booklet on peripheral artery disease discusses this topic in detail and its treatment. Readers can order a copy by writing: Dr. Donohue – No. 109, Box 536475, Orlando, FL 32853-6475. Enclose a check or money order (no cash) for $4.75 U.S./$6 Can. with the recipient’s printed name and address. Please allow four weeks for delivery.

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. Readers may also order health newsletters from www.rbmamall.com.