What Is It?
We often take our tears for granted. Actually, the proper lubrication of the eyes is complex and necessary for healthy eyes. There are three layers to the tear film covering the surface of the eye:
- Inner layer – made of mucous
- Middle layer – made of salty water
- Outer layer – made of oil
These three layers are made from three different glands. The inner layer is made from small mucous glands located in the conjunctiva. These glands cover the external white surface of the eye. The majority of the salty water is made in a fairly large gland located under the bone at the upper, outer edge of the eye. The fluid travels down canals to empty into the undersurface of the upper, outer eyelid.
The oil is made mostly in medium-sized glands located along the eyelid margin. These empty just behind the eyelashes. All three layers are necessary for making a proper tear. When one or more layer is inadequate, the result can be a dry eye.
Signs and Symptoms
The most common symptoms are: tired eyes (a desire to close them), irritation, a foreign-body sensation, burning, stringy mucous, and blurring of the vision that changes with blinking (often when driving or reading). Pain can be a problem for severe dry eyes. Often patients will complain of watery eyes. This is usually from an over action of the large salty-water gland, trying to make-up for a lack in the other layers. Thus, the most common cause of a watery eye is actually dryness.
On exam the tear film of the eye can often be seen to break-up too quickly. The oily layer should keep the tear stable for at least 10 seconds. Small defects in the cornea may be present. These tiny dots stain with dye, and are more common at the bottom of the cornea. The inferior cornea is where the most drying occurs.
Mucous builds up because the natural washing that occurs from blinking and tearing is defective. In severe cases a Schimer test may be used. This involves placing a strip of standard filter paper inside both lower lids. The amount of wetting is checked at 5 minutes and compared with normal.
Dry eyes may be secondary to other problems in the body. These might include certain diseases: rheumatoid arthritis, lupus,scrcoid, thyroid disease, kidney disease, and Sjogrens Syndrome. In some of these diseases, the water gland becomes atrophies.
Dryness might also be aggravated by certain medications. High blood pressure medication, chemotherapy agents, antidepressants, and many others may make the symptoms worse. Eye/eyelid conditions may cause or aggravate dry eyes. Loose or sagging eyelids or prominent eyes allow more exposure for drying. Blepharitis (granulated lids) cause decreased oil production. It is caused by a defect in those oil glands along the lid margin. A common cause of dry eye is the natural decrease in oil production with age. Most people over age 70 have some symptoms of dryness.
The mainstay of treatment for dry eyes, no matter the cause, is tear substitutes. These drops must be used regularly and frequently. For example: 3-4 times a day for mild cases or even every 30 minutes for severe cases. The drops can be found over-the-counter and may or may not have a preservative. Patients eyes can become sensitive to a preservative over time. However, preservative-free agents are more expensive and cumbersome to use. Also, the drops range from thin to very thick. The thin ones do not blur the vision as much, but also do not last as long. The moderately thick ones do blur the vision for several minutes, but stabilize the tear film much longer.