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Dry Eyes and Crocodile Tears

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					When we think of tears, we usually think of sadness, grief, joy or other strong
emotions. The phrase "Not a dry eye in the house" sums up our reaction to weddings,
funerals and other life-changing events. Movies that make us cry even have their own
special name: weepies. But did you know that the tears we weep when we're feeling
blue are different from the ones we shed when we chop an onion? Or that, even
though crocodiles can't cry, there's a real medical condition called Crocodile Tear
Syndrome? This month, it's time to get clear about tears.

Cheers for Tears

Human beings need to cry. Tears are a liquid that cleans, nourishes, lubricates and
protects the eyes. Without tears, the outer covering of the eye would be damaged due
to dryness, and the cornea would not receive the oxygen and nutrients it needs to
function, nor would its waste products be flushed away.

There are three basic kinds of tears:

Basal tears maintain the health of the cornea by keeping it wet and free of dust. These
tears are surprisingly complex, containing among other substances lipids, glucose,
sodium, potassium and an enzyme called lysozyme, also present in our saliva, which
is crucial to eye health. Some of these substances serve an immune function by
protecting against bacterial infection.

Reflex tears are the body's way of expelling foreign particles (dirt, dust) or other
irritants, such as onion vapors, tear gas or pepper spray. The reason onions are an
irritant is that they contain a compound that, when it encounters water in our tear
ducts, creates sulfuric acid! (Next time you're cooking, try slicing the onion in the
sink under running water.)

Emotional tears, brought on by pain, stress or strong feelings, have a different
chemical makeup than other tears. Emotional tears may be the body's way of
expelling excess hormones. Crocodile tears are not real tears (not even for crocodiles).
Instead, the phrase means "to pretend a sorrow that one doesn't in fact feel, to create a
hypocritical show of emotion," according to the Web site World Wide Words. The
idea originated as far back as the 13th century and stems from the mistaken belief that
crocodiles wept while eating their prey. Crocodile Tear Syndrome, however, does
exist. It is a rare outcome of recovery from Bell's Palsy: faulty regeneration of the
facial nerve responsible for the salivary and tear glands causes patients to cry while
eating (even, perhaps, when eating crocodile).

How Dry I Am

People who suffer from a condition called keratitis sicca, or "dry eye," know how
important tears are. Dry eye sufferers endure stinging, itching, burning, blurry vision,
or light sensitivity; the condition also makes the eyes feel scratchy and gritty, as if
there is a speck of dirt that won't go away. Ironically, this condition may actually
cause the eyes to respond with reflex tears, which do not help the problem, as they
don't contain the lubricating substances necessary to alleviate the dryness.

One of the most common causes of dry eye is aging, due to a decrease in tear
production as we get older. Other causes include a reaction to certain medications,
including antihistamines, and environmental factors such as wind, smoke, heating and
air-conditioning. Contact lens wearers also report an increase in dry eye, as do those
who've undergone LASIK surgery.

				
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posted:1/21/2011
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