Dry Eye Syndrome
Dry eye syndrome is one of the most common problems treated by eye physicians. Over ten million Americans suffer from dry eyes. It is usually caused by a problem with the quality of the tear film that lubricates the eyes.
Tears are comprised of three layers. The mucus layer coats the cornea, the eye's clear outer window, forming a foundation so the tear film can adhere to the eye. The middle aqueous layer provides moisture and supplies oxygen and other important nutrients to the cornea. This layer is made of 98 percent water along with small amounts of salt, proteins and other compounds. The outer lipid layer is an oily film that seals the tear film on the eye and helps to prevent evaporation.
Tears are formed in several glands around the eye. The water layer is produced in the lacrimal gland, located under the upper eyelid. Several smaller glands in the lids make the oil and mucus layers. With each blink, the eyelids spread the tears over the eye. Excess tears flow into two tiny drainage ducts in the corner of the eye by the nose. These ducts lead to tiny canals that connect to the nasal passage. The connection between the tear ducts and the nasal passage is the reason that crying causes a runny nose.
In addition to lubricating the eye, tears are also produced as a reflex response to outside stimulus such as an injury or emotion. However, reflex tears do little to soothe a dry eye, which is why someone with watery eyes may still complain of irritation.
Dry eye syndrome has many causes. One of the most common reasons for dryness is simply the normal aging process. As we grow older, our bodies produce less oil – 60% less at age 65 then at age 18. This is more pronounced in women, who tend to have drier skin then men. The oil deficiency also affects the tear film. Without as much oil to seal the watery layer, the tear film evaporates much faster, leaving dry areas on the cornea.
Many other factors, such as hot, dry or windy climates, high altitudes, air-conditioning and cigarette smoke also cause dry eyes. Many people also find their eyes become irritated when reading or working on a computer. Stopping periodically to rest and blink keeps the eyes more comfortable.
Contact lens wearers may also suffer from dryness because the contacts absorb the tear film, causing proteins to form on the surface of the lens. Certain medications, thyroid conditions, vitamin A deficiency, and diseases such as Parkinson's and Sjogren's can also cause dryness. Women frequently experience problems with dry eyes as they enter menopause because of hormonal changes.
Symptoms:
- Itching
- Burning
- Irritation
- Redness
- Blurred vision that improves with blinking
- Excessive tearing
- Increased discomfort after periods of reading, watching TV, or working on a computer
Detection and Diagnosis
There are several methods to test for dry eyes. The doctor will first determine the underlying cause by measuring the production, evaporation rate and quality of the tear film. Special drops that highlight problems that would be otherwise invisible are particularly helpful to diagnose the presence and extent of the dryness.
Treatment
Your ophthalmologist is often able to diagnose dry eye by simply examining the eyes. Sometimes tests that measure tear production may be necessary. Such tests may involve placing filter-paper strips under the lower eyelids to measure the rate of tear production under various conditions.
Dry eye is sometimes treated using eye drops called "artificial tears." Artificial tears are available without a prescription. You may want to try several brands to find the one that you like best. Preservative-free eye drops are available if you are sensitive to the preservatives in artificial tears. If you need to use artificial tears more than every two hours, preservative-free brands may be better for you. Solid lid inserts that gradually release lubricants during the day may also be beneficial for some people.
Some patients with mild dryness may benefit from blinking more frequently, especially when reading, driving, or watching television.
Conserving the tears in your own eyes is another approach to keeping the eyes moist. Tears drain out of the eye through a small canal into the nose (that is why your nose runs when you cry). Your ophthalmologist may close these canals either temporarily or permanently. This closure conserves your own tears and makes artificial tears last longer.
Other methods may include steps to prevent the evaporation of tears. In winter, when indoor heat is on, a humidifier or a pan of water on the radiator will add moisture to dry air. Wrap-around glasses (illegal to wear while driving in some states) may reduce the drying effect of the wind. Anything that adds to dryness such as an overly warm room, hair dryers, or wind should be avoided by a person with dry eye. Smoking is especially bothersome. Some people with dry eye complain of "scratchy eyes" upon awakening. This symptom can be treated by using an ointment at bedtime. Use the smallest amount of ointment necessary for comfort, since the ointment can cause your vision to blur temporarily.
Dry eye caused by a lack of vitamin A in the diet is rare in the United States, but is more common in poorer countries. Ointments containing vitamin A can help dry eye caused by this unusual condition. Vitamin A does not seem to help people with ordinary dry eye.
