Dry eye: the gift of tears
Ann M. Bajart
“If you have tears, prepare to shed them now,” Mark Antony said, uncovering die corpse of Julius Caesar. Like Shakespeare, most people associate tears with times of grief and rage. But the fact is that tears protect, lubricate, and cleanse the surface of the eye with every blink.
About 40% of Americans do not consistently produce enough tears to keep their eyes comfortable. Symptoms of dry eye include stinging or burning, scratchiness, stringy mucus in or around the eyes, fatigue after short periods of reading, and difficulty wearing contact lenses.
These problems occur when the tear film coating the eye breaks down and patches of the cornea dry out. The thin, transparent tear film consists of layers of oil, water, and mucus. The superficial oil (lipid) layer maintains a smooth outer surface and slows evaporation of the middle layer, which is 98% water plus small amounts of proteins and salts. Without lipid protection, this aqueous layer would evaporate 10-20 times faster than it should. The watery solution washes away irritants and foreign particles and bathes the cornea with antibacterial proteins.
The innermost layer is made up of mucus, which helps tears adhere to the surface of the cornea and spread evenly over the eye. Without this sticky coating, tears would bead up like rain on a freshly waxed car.
Although ophthalmologists diagnose most cases of dry eye by interviewing the patient and examining the eyes, tests that measure tear production are sometimes used. The Schirmer tear test, for example, involves briefly placing filter-paper strips inside the lower eyelids to measure the rate of tear production.
Aging is the most significant cause of dry eye: tear production at age 65 is about 60% less than at 18. Other contributing factors include disruption of the blinking reflex and exposure to sun, wind, smoke, indoor heating, and air conditioners.
Women, who are more likely to have this condition than men, often develop it after menopause. Regular use of certain medications such as diuretics, antihistamines, or sleeping pills can cause or worsen eye dryness in either sex. A shortage of tears often becomes apparent after someone begins wearing contact lenses, which speed evaporation and may irritate the eye.
Some people’s dry eyes are symptoms of a systemic disease such as rheumatoid arthritis or lupus. For example, a combination of dry eyes, dry mouth, and joint inflammation is the hallmark of a chronic disorder known as Sjogren’s syndrome.
Going with the flow
There are two major therapies for dry eye: replacing the tears or conserving them. For Spuds MacKenzie? Mild cases can usually be treated successfullly with topical tear substitute – eye drops that mimic the natural tear film. If the condition is chronic and lubricating drops have not relieved symptoms, minor surgery aimed at conserving natural tears may be recommended.
Dry eye sufferers can also take simple steps to slow the evaporation of tears. People who smoke find that giving up the habit provides considerable relief. It also helps to avoid direct wind, air conditioning, or hair dryers as much as possible. A humidifier, which adds moisture to dry air caused by indoor heat in the winter, may be a wise investment for people with this problem. And those who wake up with scratchy eyes in the morning should ask an ophthalmologist about using a bland lubricating ointment at bedtime.
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