From The Eye Book published by The Johns Hopkins Press
The diagnosis: you have dry eyes. And it’s no fun having eyes that often burn or feel tired, gritty, irritated, itchy, or sticky.
For people who suffer from it, having dry eyes can be a constant source of discomfort that makes it difficult to get through the day. Having dry eyes means you’re infinitely more sensitive to everything around you. Symptoms get worse, for instance, whenever it’s windy, when the air quality is poor, or when the humidity is low. Indoors, heating and air conditioning can wreak havoc on both your comfort and your vision.
Having dry eyes is a chronic problem, and currently there’s no cure. But there are good treatments--drops, ointments, punctal plugs, and even “bandage” contact lenses--that can make you feel almost as good as new by helping control the dryness and the miserable symptoms it can produce. Before we cover how these work, let’s take a moment to consider the problem.
Why Are My Eyes Dry?
There are two basic problems: either you’re not making enough tears, or the tears you’re making aren’t as good as they used to be. Occasionally dry eyes may be caused by a third problem: the eye itself can’t get the tears where they need to go.
Not Making Enough Tears
Perhaps your eyes don’t make enough tears. This condition, called keratoconjunctivitis sicca (KCS), usually occurs in both eyes but can be worse in one eye than the other.
One of the most common causes of tearing deficiency is simply age. Like skin and hair, our tears tend to “dry up” slightly as we get older; we just make fewer tears. For most of us this decrease isn’t terribly noticeable, but for some people tear production can drop off significantly--enough to produce the classic dry-eye symptoms of irritation, redness, grittiness, burning, and eye fatigue. (KCS is also more common in older women than in other groups, probably because of the hormonal changes that occur with age.)
Other health problems or issues can hamper tear production. One of these is injury to the lacrimal glands, from infection or trauma; the effect of the injury may be temporary or permanent. Another is Bell’s palsy, a condition that affects the facial nerves; its effects may also be either temporary or permanent. People with this ailment are often unable to close one eye or blink on one side of the face, and that eye also produces fewer tears. As you may imagine, the combination of not being able to blink and making fewer tears causes major problems by exposing the corneal surface to excessive drying, resulting in exposure keratitis. A decrease in corneal sensitivity that stimulates the lacrimal gland to produce tears can also lead to a dry eye and can be seen with refractive surgery (i.e., LASIK), cataract surgery, contact lens wear, and abuse of topical anesthetic eye drops.
Autoimmune disorders can impede tear production. Sjögren’s syndrome is the miserable trio of symptoms--dry eyes, dry mouth, and joint pain--that may be associated with other autoimmune disorders, such as rheumatoid arthritis, systemic lupus erythematosus, and scleroderma. (The term secondary Sjögren’s syndrome is used to describe dry eyes associated with any other disease.) Other systemic (“whole body”) diseases, such as sarcoidosis, leukemia, lymphoma, and chronic thyroid problems, often diminish tear production as well.
Occasionally medications decrease the tear-making ability in some people. For instance, as you may already know too well, antihistamines and decongestants for allergies and colds dry out everything--eyes in addition to sinuses. Diuretics, taken to lower blood pressure and ease water retention, may decrease tear production. Hormone replacement therapy and even birth control pills also can lead to dry eyes. Other potentially eye-drying medications include certain eye dilators (atropine and scopolamine), motion sickness inhibitors (scopolamine), tricyclic antidepressants (amitriptyline, desipramine, imipramine, nortriptyline), oral acne medications (Accutane, tetracycline), and opiate-based pain medications (morphine). Note: Of course, even though these and other drugs may produce dry eyes, this isn’t reason enough to stop taking them. If the eye-drying side effect really bothers you, talk to your doctor. It may be possible for you to switch to an alternative medication.
The Old Tears Ain’t What They Used to Be
Even if your tear production is just fine, your eyes can still be dry if the quality of tears is poor. Remember the ingredients in each tear; they’re all important, and when the balance of them is off, your tears (and your eyes) may suffer as a result.
Diseases in the eye or body can cause a drop in either the mucin or the lipid portion of tears. Vitamin A deficiency, trachoma (an infection that’s very common in the Middle East), Stevens-Johnson syndrome (an inflammation of skin and mucous membranes causing scarring and dysfunction of those membranes), and chemical burns of the eye all cause a breakdown and scarring of the conjunctiva and sclera. This in turn destroys goblet cells and causes the production of mucins to dwindle. Without mucins, tears don’t hold up as well; they break apart much more quickly on the surface of the cornea. (Imagine the difference in texture between watercolor and oil-based paint.) As a result, the cornea tends to dry more quickly.
One of the most common eye diseases to obstruct lipid production by the Meibomian glands is blepharitis, an infection of the eyelid (see chapter 11 in The Eye Book). When the eyelid becomes infected, bacteria (and the immune reaction they trigger) cause the Meibomian glands to clog and shut down. Again, the result is a more watery (and less oily) product: tears that evaporate much more quickly from the eye. Even worse, as these lipid-lacking tears evaporate, they leave behind a greater-than-normal concentration of salt, and salt burns the eyes. Recalcitrant blepharitis and dry eyes are often seen when rosacea (yes, the same rosacea that caused zits on your face when you were a teen) involves the eyelid margins. This condition affects people ages 30-60, more often affects women than men, and is often associated with Meibomian gland dysfunction of the eyelid. Besides contributing to tear dysfunction and a dry eye, rosacea can cause other ocular conditions such as recurrent chalazion, chronic conjunctivitis, severe stromal keratitis, marginal corneal ulcers, and uveitis. Just like when you were a teen, the antibiotic tetracycline (or its derivatives minocycline and doxycycline) can be helpful for treating rosacea affecting the eyelids, both orally and topically. Topical steroids may be necessary for some of the ocular complications caused by rosacea.
Another common cause of dry eye from lack of lipids is sleeping with your eyes open (nocturnal lagophthalmos). Sleep is the body’s great restorer, a chance for everything, including eye moisture, to be replenished. If you don’t close your eyes fully when you sleep, exposed parts of your eye tend to dry out. Symptoms are usually at their worst when you wake up, and they get better during the day as normal blinking returns moisture to the eye. This is a fairly easy-to-treat problem; often, simply adding humidity to the room where you sleep with a humidifier and applying an artificial tear ointment before bedtime are enough to keep the eye moist overnight. (Nocturnal lagophthalmos is also a common problem for people with Bell’s palsy; the lid of the disabled eye doesn’t close at night, and this makes the already-dry eye feel even worse. But taping the eye closed at night, along with the use of artificial tear ointments, can help replenish eye moisture.)
Distribution Problems
With tears, as with any complicated manufacturing system, the breakdown may come not in quality control or production but in shipping or distribution. Sometimes the tears themselves are just fine, and they’re made in adequate amounts, but the eye itself can’t get them where they need to go.
Irregularities on the surface of eyelids or corneas, for instance, can cause dryness even if tear production is adequate. If the eyelids are scarred significantly--a problem in chronic blepharitis--the lid can’t distribute tears evenly across the surface of the cornea; think of faulty wiper blades trying to sweep a car’s windshield. Similarly, if the cornea is scarred, the lid can’t do a good job of spreading tears. In either case, the tear-deprived surface of the cornea becomes parched.
Growing older can also cause changes in the musculature and shape of our eyelids, occasionally causing them to sag or turn outward (ectropion) or inward (entropion; see chapter 11). These problems also disrupt how tears are spread across the eye and how they flow out of the eye. Often, when this happens, people experience symptoms of dryness. A person may also have tears that stream down his or her face (This may sound like a flat-out contradiction of a diagnosis of dry eyes: after all, how can your eyes be dry when they’re literally overflowing with tears? But think of water pouring down from a damaged gutter in a heavy rain. Water just isn’t getting where it is supposed to go.)
Finally, some people just don’t do a good job of blinking (a common symptom of Parkinson’s disease); consequently, tears don’t get spread across the eye as they should. With each complete blink, the upper lid should meet the lower lid. Partial blinking leaves the lower portion of the cornea constantly exposed and increases dryness over the course of the day.
For more information about dry eyes and its treatment, you can refer to The Eye Book published by The Johns Hopkins Press
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