Dry eye syndrome (also known as keratoconjunctivitis sicca or KCS) is one of the most common ocular conditions. It is characterized by decreased production of natural tears. Most cases are mild, but it often can affect your comfort and ocular health. Despite greater understanding of tear film production, the underlying cause of dry eyes is usually unknown. However, various treatments are available to afford some relief from their chronic ocular problem.

The Normal Tear Film
The tears form a moist layer over the surface of the eye, including the cornea and conjunctiva. Since the tear layer is the outermost surface of the eye, it acts as an interface between the eye and the outside environment. There are several important functions of the tear film. It moistens and protects the surface cells (epithelium). Without that moisture, the cells can harden and look more like the skin over the rest of your body. The tear film also provides a smooth, transparent surface that helps focus light entering the eye, and is necessary for sharp, clear vision. Our tears also serve as a vehicle for oxygenation and nourishment of the ocular surface. Finally, the tear film contains several substances that help protect the ocular surface against infection.

The film is comprised of three layers, each essential to maintaining the health of the eye (FIG. 1). Abnormalities of any of these layers can cause a tear dysfunction problem. The innermost layer is made of mucin produced by cells in the conjunctiva, and helps the tears spread smoothly over the ocular surface (wettability). The thick middle layer is composed primarily of water, and is produced by the lacrimal gland. Finally, the outer lipid layer, produced by the meibomian glands, enhances the stability of the middle aqueous layer by retarding tear film evaporation.

A deficiency in any one of these layers can result in the symptoms of dry eye, although the dry eye syndrome most commonly results from an insufficient aqueous layer. It may also result from an abnormal lipid or mucins layer or from problems in eyelid function and blinking. Normally, tears are produced constantly by the lacrimal glands. Tear production increases in response to dryness, irritation, or emotions. The tears flow over the ocular surface, being spread and smoothed by the blinking of the lids, and eventually drain away from the eye through the lacrimal ducts at the inner corner of each lid, into the nose.

What Are The Symptoms of Dry Eye?
The most common symptoms are dryness, burning, irritation, a sandy or gritty feeling, redness, and blurred vision. These symptoms usually affect both eyes, but only one can be affected. The eyes typically get worse as the day progresses, and can become more pronounced when reading or watching TV. Some patients may be especially sensitive to dry or irritating environments, such as dry heat, warm or smoke-filled rooms, and wind. Sensitivity to light may also be reported.

How is Dry Eye Diagnosed?
The signs of dry eye are often subtle, and the eye doctor may not make the diagnosis unless he or she specifically tests for it. The following are often used and can be very helpful in detecting dry eyes.

Vital Dry Stains
Rose bengal (rose colored) and lissamine green dyes adhere to the ocular surface where it is dry or irritated. The amount and pattern of staining can tell the doctor what is causing your symptoms.

Test of Tear Production
These tests involve placing a small strip of paper or a thread under the lower lid and measuring how much tears it absorbs over a small period of time. These tests are simple and make the diagnosis if the result is low. However, they often miss mild cases of dryness.

Tear Break-up Time (BUT)
The tear break-up time (BUT) is a direct measure of the stability of the preocular tear film. A normal tear film with sufficient lipid, aqueous, and mucinous layers begins to break up, or show signs of discontinuity, after approximately 10 seconds. This process is generally accelerated in patients with dry eyes.

What is Sjogren's Syndrome?
Sjogren’s syndrome is the combination of dry eyes and dry mouth or dry eyes and a systemic autoimmune disease, such as rheumatoid arthritis or lupus erythematosis. The combination of dry eyes and dry mouth alone is called primary Sjogren’s syndrome, and can be associated with inflammation elsewhere in the body. A thorough general physical examination and some blood tests are necessary to make the diagnosis of primary Sjogren’s syndrome. In most cases the only treatment is of the ocular and mouth dryness.