Tears bathe the eye to keep it moist and remove irritating or infectious particles.  Clear vision depends on a healthy layer of tears covering the surface of the eye.  When the eye cannot produce enough tears or produces abnormal tears, dryness is the result.
Tears have three major components.  An oily outer layer is produced by the meibomian glands that line the inner eyelid.  This layer keeps the watery layer from evaporating away and smooths the surface of the tear film.  Meibomian gland dysfunction is common in patients with blepharitis, an inflammatory eyelid condition.  The watery layer is produced by the lacrimal glands and is made at a slow, steady rate.  Large quantities of tears can be produced in response to eye irritation or emotion.  The inner mucus layer is produced by the conjunctiva.  The mucus allows the watery layer to stick to the eye and spread evenly over the surface.

Dry eyes cause stinging and burning, a gritty sensation, stringy mucus production, and paradoxically, excess tearing.  If the tears that are supposed to maintain the correct lubrication of the eye are not effective, the resulting irritation will trigger the lacrimal glands to produce a large quantity of the watery component of tears.  These excess tears overwhelm the tear drainage mechanism and result in tears spilling over onto the cheeks.  Mild dry eye symptoms can manifest as irritation from smoking or exposure to wind or dashboard heaters, discomfort after short periods of reading or computer work, or with contact lens use.   It is common for the symptoms to begin or become worse in the afternoon or evening.

Dry eyes are more common with age due to decreased tear production.  This is particularly true of postmenopausal women and may be related to hormonal changes.  People with an inflammatory eyelid condition called blepharitis often have associated dryness.  Patients with certain autoimmune diseases like rheumatoid arthritis and lupus are at high risk for reduced tear production.  Sjögren’s syndrome is a chronic autoimmune disease that causes dry eyes and dry mouth.  Radiation treatments to the head can result in decreased tear production.  The refractive procedure LASIK causes dry eyes because of damage to nerves in the eye.  The dry eye symptoms in this case are usually temporary, resolving as the injured nerves regenerate over a period of months.  Incomplete eyelid blinks, cause uneven distribution of the tears over the surface of the eye and some parts of the eye can dry out.  A similar situation occurs when the surface of the eye is irregular from scars on the cornea or conjunctiva.  Tissues that are higher than the remainder of the surface of the eye are vulnerable to drying because the tear film is thinner over them.  Tasks that require intense visual concentration such as driving, reading, and computer use lead to dryness because of a decrease in the rate of blinking.

A number of common medications can reduce tear production.  These include diuretics (water pills) used for high blood pressure, heart failure, and chronic leg swelling; beta-blockers used for heart disease and high blood pressure; antihistamines used for allergies; birth control pills; some antidepressants; non-steroidal pain relievers; and isotretinoin, used to treat acne.

Complications of dry eyes include blurry vision, scarring of the surface of the eye, and an increased risk of developing eye infections.  These complications are uncommon unless the dryness is severe and untreated.  For most people with mild or occasional dryness, over-the counter artificial tears used up to four times a day are effective to relieve the symptoms.  These preparations mimic natural tears.  There are many brands on the market that vary in thickness and components.  Finding the one that works the best may require trying several different ones.  Preservative-free tear drops are available for people who are sensitive to the preservatives or who need drops more than four times a day for relief.  These drops can be safely used as often as needed.  Ointments are very thick and tend to blur vision.  They are appropriate for use just before bedtime and can relieve irritation that is present on waking up.

To minimize evaporation of tears, which tends to be worse in arid environments, use a humidifier.  This is particularly helpful in the winter and when forced hot air heat is used.  A pan of water can be set on a woodstove.  Wrap-around glasses and a hat with a brim can reduce the drying effect of the wind.  Avoid tobacco smoke and other irritants.  Take periodic eye breaks when reading, working at the computer, or driving for long periods of time.  Close your eyes for several seconds, then blink repeatedly for several seconds to redistribute the tears over the surface of your eyes.  Keep your computer screen below your eye level.

If a medication is causing or aggravating your dry eyes, changing to another medication may be recommended.  Eyelid problems with an anatomic abnormality or incomplete blinks may need a surgical procedure to resolve the dryness.  Treatment of underlying blepharitis is usually effective to relieve the associated dry eye symptoms.  Punctal plugs are small plastic devices that close off the tear drainage pathway, keeping the tears that are produced on the surface of the eye for a longer period of time.  Lacrisert® inserts are sustained-release tear substitutes that are placed between the lower eyelid and the eye once or twice a day.  They can be used by people with more severe dry eyes who cannot use artificial tears as frequently as they are needed.

Patients with dry eyes from an auto-immune disease as well as many patients with moderate dry eyes from other causes respond favorably to anti-inflammatory medication.  Restasis® is an immunomodulatory agent that gradually decreases inflammation in the glands that produce tears.  It increases the production of natural tears and helps to normalize the components of those tears.  This medication takes several weeks to begin to be effective, and the maximum effect can take months to achieve.  Most patients find that their need for artificial tears decreases with regular use of Restasis®.

The Tear Lab Osmolarity System is an in-office test to determine the health of the tear film.  It assists in making a diagnosis of dry eyes and is helpful in monitoring response to treatment over time.  THis painless test takes less than a minute to perform.