If our eyes are healthy, we're producing tears all the time and not noticing it very much, if at all. We need a thin layer of tears to lubricate, protect, and nourish the fronts of our eyes. That "tear film," as ophthalmologists call it, isn't just salty water but a complex mixture of substances produced and maintained by several glands and structures in and around the eyes. If the tear film degrades, we experience dry eyes. The symptoms are familiar to many of us: irritation, scratchiness, a burning sensation. Sometimes vision is affected, getting blurry off and on.
Mild cases — and many are — can be treated rather easily with any of over a dozen different over-the-counter products. In a change from the past, dry eyes are now seen as having an inflammatory component, not just a loss of moisture. To combat the inflammation, some ophthalmologists prescribe drops that contain a very small amount of cyclosporine if the over-the-counter products don't work. Cyclosporine is a drug that organ transplant recipients take to suppress the immune system so the organ is less likely to be rejected.
Older and drier
Dry eyes used to be thought of as a simple problem of not enough tear production, too much tear evaporation, or some combination of both. Dry eyes may still begin that way, but now the thinking is that localized inflammatory processes get started as the tear film loses moisture.
Air conditioning during the summer — and indoor heat during the winter even more so — makes the air inside our homes bone-dry, so water in tear film and other bodily surfaces evaporates easily. Blinking levels out and replenishes the fatty outer layer of the tear film, and normally we blink every 10 seconds or so. Activities that decrease that rate — watching television, working at a computer, driving a car — can cause dry eyes because they slow down the blink rate.
Age is a factor: the older orb tends to be a drier one because the lacrimal and other glands become less productive. And with age, lower eyelids may sag, so they don't form a good seal over the eye. In general, women are more prone than men to dry-eye problems.
Autoimmune diseases, conditions in which the immune system turns on the body instead of throwing itself at invading infections as it is supposed to, can affect tear film ingredients and cause dry eyes. Lupus and rheumatoid arthritis are two such autoimmune diseases.
Dry eyes are also a side effect of some commonly used medications, including antihistamines, beta blockers, and the selective serotonin reuptake inhibitor (SSRI) antidepressants, such as citalopram (Celexa) and fluoxetine (Prozac). Some over-the-counter eye drops contain benzalkonium chloride, a preservative that can dry out eyes and have other side effects.
Dry eyes are a common side effect of LASIK to correct nearsightedness and farsightedness, although it's usually temporary. Contact lenses reside within the tear film, and dry eyes are one of the main reasons some people can't wear contact lenses or can only do so on a limited basis. Sometimes switching contact lens solutions or trying lenses made out of a different material can help.
Going by symptoms
There isn't any one specific test to diagnose dry eyes. Most ophthalmologists will as a matter of course examine the eyes with a slit lamp, the device with the chin rest and the bright light that the doctor uses to peer into our eyes. Eye drops with special stains can be used to evaluate the health of the eye surface and gauge the stability of the tear film.
Frequently, though, the eye examination and test results are secondary in the diagnostic workup, especially if the problem is mild. Symptoms and the patient's history are often the key pieces of information in arriving at a diagnosis.
Not as good as the real thing
If the source of the problem is dry air, using a humidifier can make a big difference. Limiting screen time (television, computer monitors), which is bad for many body parts, not just those we see with, can also help.
But the first-line treatment for most people with dry eyes remains an over-the-counter topical treatment of some kind, typically drops. These products are referred to as artificial tears. The starting dose is usually a drop in each eye four times a day.
The prescription cyclosporine drops are usually used after patients have tried the over-the-counter products. Cyclosporine drops take some time to work — between six and eight weeks in most cases. Price is a drawback: sold under the brand name Restasis, they cost about $250 a month. Moreover, people may have to use them indefinitely.
November 2010 update
As the eyes age, problems with vision become more common. Learn how to recognize the risk factors and symptoms of specific eye diseases — cataract, glaucoma, age-related macular degeneration, and diabetic retinopathy — and what steps you can take to prevent or treat them before your vision deteriorates.Learn more »