Question: I recently saw my eye doctor because I suddenly became very sensitive to light. He said that it was caused by a condition called "Adie's pupil." My right pupil is much larger than my left and it won't get smaller in bright light. Otherwise, I see fine. He gave me eye drops, but didn't really know what caused it. Is it curable?

Answer: Adie's pupil is a condition likely from a viral infection affecting the nerve fibers that constrict the pupil in bright light. Other than being very sensitive to bright light in the affected eye (because the pupil can't properly constrict to limit the amount of light entering the eye), vision is unaffected. We're not entirely sure why it happens, or why it seems mostly to affect women in the 25-45 age group.

Adie's pupil can be treated with pilocarpine eye drops prescribed by an ophthalmologist. Sunglasses in bright light are a good idea, too. Just as mysteriously as Adie's can appear, it can gradually disappear over time. In some folks, it may be there to stay.

How antidepressants elevate a person's mood

Q: Can you explain how antidepressants work in the brain to help with depression?

A: When a person is depressed for a long time, chemicals that normally generate signals of well-being and good mood in the brain get terribly out of balance. Cells in the brain's prefrontal area "talk" to one another via chemical transmitters. Those involved in mood are serotonin, norepinephrine, and dopamine. These three chemicals are in short supply in a person with major depression. Antidepressants work by raising the levels of one or more of these transmitters to help bring your brain back into balance. Antidepressants, along with professional therapy, help you to gain insight into the cause of your depression and facilitate a cure. Antidepressants are not "magic pills."

If it seems like some people are happier than others, there may be an explanation on a genetic level. A gene that regulates the movement of serotonin in the brain has been labeled the "happiness gene" by British researchers with the London School of Economics. There are four ways in which this gene may be expressed. Those with the most DNA coding for the happy gene feel happiest because there are more serotonin transporters within nerve cell membranes. Those with the short version of the happy gene were most likely to describe themselves as dissatisfied with their life.

Mitchell Hecht is a physician specializing in internal medicine. Send questions to him at: "Ask Dr. H.," Box 767787, Atlanta, Ga. 30076. Due to the large volume of mail received, personal replies are not possible.