Q: Why do doctors dilate your eyes for an exam, and are there any drops to reverse the dilation?

Doctors use a class of drugs called mydriatics to widen the pupil, enabling them to see the retina and optic nerve. Depending on the drug, mydriatics work by paralyzing the muscle that makes the pupil smaller or by stimulating the muscle that dilates the iris.

There is an anti-dilation drug, dapiprazole, which blocks stimulation of the muscle that widens the iris. In a 1994 clinical study, published in the journal Optometry and Vision Science, the drug was tested in one eye in 30 subjects who had been given drops containing the dilation drug tropicamide.

Average recovery time was significantly less in the treated eyes.

Dr. Stanley Chang, chairman of ophthalmology at New York-Presbyterian Hospital/Columbia University Medical Center, said that dapiprazole was popular with his patients and that it usually brought the pupils down in about an hour. But he added that the drug was now off the market in this country; he said he was not sure why.

"However, the effect of most dilating drops wears off in about two hours, and the patient is able to resume reading.

Q: Is there any science behind the old saying "Don't go to bed angry?"

According to a study in The Journal of Neuroscience, scientists found there might be a nugget of truth to it: Going to sleep after experiencing negative emotions appears to reinforce or "preserve" them.

The scientists recruited 106 men and women and exposed them to images that elicited various emotions. In some cases, the emotions were negative - for instance, after an unsettling image of an accident or a traumatic scene. In other cases, the images produced positive or neutral emotions.

The researchers then looked at what happened when the subjects were shown both new images and the previous ones 12 hours later - either in the morning after a night of sleep or at the end of a full day of wakefulness. And they measured brain activity during the rapid eye movement, or REM, phase of sleep, when dreams occur.

The scientists found that staying awake blunted the emotional response to seeing the upsetting images again. But when the subjects were shown the disturbing images after a night of sleep, their response was just as strong as when they had first seen them, suggesting that sleep "protected" the emotional response.