HOW COME? Preferred winking eyes

How come my husband can only wink with one eye? asks a reader.

Blinking bathes our eyes in fluid, washing away dust and keeping them moist. Winking is social, underlining shared opinions, attraction, jokes and mini-conspiracies (Dad: "Why no, I didn't let little Johnny have another cookie." Side wink at giggling Johnny, lips covered in crumbs).

Most people have a preferred winking eye. Others can wink only with one. And some find it hard to wink at all.

Scientists note that human beings have many such "asymmetries." Depending on what we're doing, one side of the body is more dominant or responsive. The asymmetry we notice most, of course, is handedness.

Which hand do you write with? Most people are righthanded, but at least 10 percent of us are lefties. And most people also have a dominant foot to kick a ball with.

Although we don't notice it as often, most of us have a dominant eye, too. Your dominant eye is the one you naturally press to a camera viewfinder, or use to peer through a telescope eyepiece in the backyard. It's the eye the brain prefers for visual input.

Hand movements are controlled by opposites sides of our brain, the right hand controlled by the left hemisphere and vice versa. But the brain-eye connection is more complicated. The brain's hemispheres are in charge of opposite halves of our field of vision. So each hemisphere controls its own half of each eye's retina.

When it comes to eye dominance, studies show that there's no connection to handedness. (Which is how a person can be righthanded, but "left-eyed.") According to researchers, the right eye is the dominant one in about two-thirds of us, the left in nearly one-third. And some people apparently don't have a dominant eye.

Try this simple test to find yours: Use the tented fingers of your hands, arms extended, to create a small opening. Look through the opening at an object across the room -- say, a doorknob. Now close each eye in turn. With your dominant eye open, the doorknob should stay in view. But with only your nondominant eye open, the doorknob should suddenly shift out of the opening.

What does eye dominance have to do with winking? Surprise: Studies show that the preferred winking eye is the nondominant eye -- the one we don't use to look through a telescope. Likewise, in a study of students who could wink only with one of their two eyes, it was the nonwinking eye that was dominant.

For more on eye dominance and how to test yours, see http://vision.about.com/od/contactlenses/ht/Eye_Dominance.htm.