Tear Production

Tears are the watery substance that bathes the eye. They form a film that keeps the cornea moist, protects the eye against infection and helps eye wounds heal. There are actually three layers to the tear film. The outer layer is the oily layer produced by the meibomian glands. This layer prevents tears from evaporating too quickly and allows tears to stay in the eye (and not run down the face). The middle of the tear film is a watery layer produced by the lacrimal gland. This watery fluid nourishes the cornea and carries away tiny particles or irritants. The inner layer of the tear film contains mucus produced by the conjunctiva (the membrane lining the inside of the eye). This layer helps the tear film spread over the surface of the eye and keep the eye moist.

Dry Eye

Dry eye is a condition characterized by a decrease in the production of tears or change in the quality of tears. As the term suggests, the surface of the eye doesn't get enough moisture, causing a scratchy or sandy feeling in the eye, stinging or burning, redness and pain. Sometimes patients with dry eye will experience a surge of excess tears after a period of eye dryness. The condition can cause blurred vision.

As we age, fluid production in the eyes decreases, causing the eyes to feel somewhat dryer. Women are affected more often than men, especially after menopause. Dry eye can also be associated with use of certain medications and rheumatoid arthritis. A condition called Sjogren's Syndrome affects the fluid-producing glands in the body and leads to dry eye symptoms.

Another cause of dry eye is Stevens-Johnson Syndrome (SJS), a condition that affects the skin and mucous membranes. It was first described by two pediatricians (A.M. Stevens and S.C. Johnson) in 1922. Patients can develop blisters on the mucous membranes. In the eyes, the blisters can lead to scars that damage the mucuous membranes and cause severe dry eye and inward turning of some of the eyelashes. Patients may experience corneal ulceration and loss of sight.

Treating Dry Eye

The main method of treatment for dry eye is use of artificial tears in the form of eyedrops. The products lubricate the eyes and help reduce dryness. Some patients may need to use the drops several times an hour.

Patients can also take steps to slow the evaporation of tears from the eyes. Wrap-around glasses reduce evaporation when outside. Indoors, humidifiers can add moisture to the air and reduce fluid loss in the eye. Hair dryers and smoke-filled rooms should be avoided. At night, patients can place moisturing ointments in the eye and cover the eye with a patch to prevent escape of moisture.

Saliva Gland Transplant

Randal Paniello, M.D., a Head and Neck Surgeon at Washington University, is using a novel procedure to treat some patients with extreme dry eye problems, called a saliva gland transplant. He says he is the first physician in the U.S. to perform this transplant.

The saliva glands are the fluid-producing glands in the mouth and throat. There are three pairs of major saliva glands: the sublingual glands (located under the chin), the submandibular glands (in the neck, under the lower sides of the front of the face) and the parotid glands (under the ears). The glands secrete saliva into the mouth through tiny ducts. There are also many minor salivary glands in the inner cheeks, mouth and throat.

Paniello removes the submandibular saliva gland, duct and the connecting vein and artery. Next, a small incision is made into the temple, above the outer corner of the eye. A small amount of muscle is removed to make room for the saliva gland. Then, the gland is placed in its new location. The artery and vein are connected to nearby vessels to provide blood flow to the gland. Finally, the end of the duct is connected inside the outer corner of the upper eyelid at the spot where tears would normally be released into the eye. The surgery takes about 8 to 10 hours and patients spend about a week in the hospital for follow-up.

The saliva gland transplant is not an exact substitute for tears. Fluid production occurs at a constant rate. Since patients can't control the flow of fluid, there are no real "tears." Saliva is a little thicker and stickier than tears. However, that turns out to be an advantage because the fluid doesn't evaporate as readily and stays in the eye longer. So far, doctors haven't seen any adverse effects from the mild digestive enzymes that are naturally present in saliva.

Paniello says removal of the saliva gland poses no problems for the patient since the other glands simply increase their own production of saliva. The nerve that controls salivation isn't moved with the gland, so patients don't experience an excess amount of fluid if the patient salivates.

Paniello says the saliva gland transplant could be useful for many patients with severe dry eye problems. However, it is not an option for patients with Sjogren's Syndrome because that disease also causes damage to the salivary glands.

More Information:

American Academy of Ophthalmology National Eye Institute