Dry Eye Syndrome
When you blink, a film of tears spreads over the eye, making the surface of the eye smooth and clear. Without this tear film, good vision would not be possible.
Sometimes people don't produce enough tears or the right quality of tears to keep their eyes healthy and comfortable. This condition is known as dry eye.
The tear film consists of three layers:
An oily layer;
A watery layer;
A layer of mucus.
Each layer has its own purpose. The oily layer, produced by the meibomian glands, forms the outermost surface of the tear film. Its main purpose is to smooth the tear surface and reduce evaporation of tears.
The middle watery layer makes up most of what we ordinarily think of as tears. This layer, produced by the lacrimal glands in the eyelids, cleanses the eye and washes away foreign particles or irritants.
The inner layer consists of mucus produced by the conjunctiva. Mucus allows the watery layer to spread evenly over the surface of the eye and helps the eye remain moist. Without mucus, tears would not stick to the eye.
Normally, the eye constantly bathes itself in tears. By producing tears at a slow and steady rate, the eye stays moist and comfortable.
The eye uses two different methods to produce tears. It can make tears at a slow, steady rate to maintain normal eye lubrication. It can also produce a lot of tears in response to eye irritation or emotion. When a foreign body or dryness irritates the eye, or when a person cries, excessive tearing occurs.
It may not sound logical that dry eye would cause excess tearing, but think of it as the eye's response to discomfort. If the tears responsible for maintaining lubrication do not keep the eye wet enough, the eye becomes irritated. Eye irritation prompts the gland that makes tears (called the lacrimal gland) to release a large volume of tears, overwhelming the tear drainage system. These excess tears then overflow from your eye.
Causes of Dry Eye Syndrome
Hormonal changes are a main cause of dry eye syndrome, causing changes in tear production. The hormonal changes associated with menopause are one of the main reasons why women are most often affected by dry eye.
Conditions that affect the lacrimal gland or its ducts — including autoimmune diseases like lupus and rheumatoid arthritis — lead to decreased tear secretion and dry eye.
Tear secretion also may be reduced by certain conditions that decrease corneal sensation. Diseases such as diabetes and herpes zoster are associated with decreased corneal sensation. So is long-term contact lens wear and surgery that involves making incisions in or removing tissue from the cornea (such as LASIK).
A wide variety of common medications, both prescription and over-the-counter, can cause dry eye by reducing tear secretion. Be sure to tell your ophthalmologist (Eye M.D.) the names of all the medications you are taking, especially if you are using:
Diuretics for high blood pressure;
Beta-blockers for heart or high blood pressure;
Antihistamines for allergies;
Since these medications are often necessary, the dry eye condition may have to be tolerated or treated with eyedrops called artificial tears.
People with dry eye are often more likely to experience the side effects of eye medications, including artificial tears. For example, the preservatives in certain eye drops and artificial tear preparations can irritate the eye. These people may need special, preservative-free artificial tears.
Another cause for dry eye is exposure to a dry, windy climate, as well as smoke and air conditioning, which can speed tear evaporation. Avoiding these irritants can offer dry eye relief.
Symptoms of Dry Eye
Dry eye symptoms usually include:
Stinging or burning eyes;
Stringy mucus in or around the eyes;
Excessive eye irritation from smoke or wind;
Discomfort when wearing contact lenses.
Dry Eye Treatment
An ophthalmologist is usually able to diagnose dry eye by examining the eyes.
Sometimes tests that measure tear production are necessary. A test called the Schirmer tear test involves placing filter-paper strips under the lower eyelids to measure the rate of tear production under various conditions.
Another way your Eye M.D. can diagnose dry eye is by putting special dye drops in the eye then studying how long it takes for dry spots to develop on the cornea. The dye test can also be used to look for certain staining patterns that show any damage to the surface of the cornea.
Source: American Academy of Ophthalmology, www.geteyesmart.com