Q. My eyes are dry a lot. Is this something common when you get older?

If your eyes seem to have become drier than normal, you should visit an eye doctor for a checkup. It's always better to have a professional examine you when you experience a troublesome bodily change.

Dry eyes are common in people older than 50 because our production of tears diminishes as we age. A lack of tears is more common among women, especially after menopause.

The tear film in your eyes has three basic layers: oil, water and mucus. Problems with any of these can cause dry eyes.

The outer layer of the tear film, which is produced by small glands on the edge of your eyelids, contains fatty oils. These smooth the tear surface and slow evaporation of the middle watery layer. If your oil glands don't produce enough oil, the watery layer evaporates too quickly, causing dry eyes.

The middle layer is mostly water with a little bit of salt. This layer, produced by the tear glands, cleanses your eyes. If the tear glands don't make enough of the watery part of tears, you get dry eyes.

The inner layer of mucus helps spread tears evenly over the surface of your eyes. If you don't have enough mucus to cover your eyes, dry spots can form on the front surface of the eye.

Tears are necessary for overall eye health and clear vision. Tears keep eyes moist and wash away debris. They also help protect the eyes from infections.

Dry eye can be caused by an inflammation or any disease that changes tears.

It can be caused by side effects from some medicines including antihistamines, nasal decongestants, tranquilizers, blood pressure medicines, Parkinson's medications, birth control pills and anti-depressants.

Women who are on hormone replacement therapy may experience dry eye symptoms. Allergies are associated with dry eye. Infrequent blinking from staring at a computer or video screen, may also lead to dry eye symptoms.

People who have had LASIK or other refractive surgery, where their corneas have reduced sensation because of incisions or tissue removal, may also experience dry eye. Also, people who wear contact lenses long term are at risk for developing dry eye.

Dry eye can damage the cornea, the clear, protective surface that covers the colored part of the eye, the iris. Permanent loss of vision from dry eye is uncommon.

(In our next column, we'll detail some treatments for dry eye.)

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