What is Dry Eye?
One of the more common causes of eye irritation is known as Dry Eye Syndrome. Dry eyes are estimated to affect 12 million Americans. The tear film which covers the surface of the eye is a complex 3 layered structure which has many functions. It is made mostly of water, but also has an inner layer of mucus, which holds the tear film to the eye surface and an outer layer of lipids (fats) which slow evaporation of tears. The tear film lubricates the eye, smoothes irregularities for better vision, washes germs and other irritating substances from the eye surface and carries oxygen to the surface of the eye. Dry eye is a label for various disorders of the tear film which may be classified into two categories: (1) decreased tear production or (2) excessive tear evaporation. Dry eye may also develop as a result of disease in the oil-producing glands of the eyelid. Regardless of the mechanism, water is lost from the tear film, making it more "concentrated". This draws water from the eye tissues, leading to further deterioration of the health of the eye surface. Eventually, dry, rough spots appear on the eye surface, which may reduce vision. In severe cases, scarring may develop.
Who is at Risk to Suffer from Dry Eyes?Dry eye becomes more common with increasing age and as body hormone changes develop. Most commonly affected are post-menopausal women. Certain autoimmune conditions, such as Rheumatoid arthritis and Sjogren's syndrome, occur together with dry eyes. Medications taken by mouth are another common cause of dry eyes. In particular, several categories of drugs are more likely to cause dry eye, including:
More rarely, there can be a genetic or hereditary cause of dry eyes. For many who have dry eyes, environmental conditions may be an important factor worsening symptoms. Most likely to cause worsening of dry eye are low humidity environments, wind, central heat or air conditioning and airplane travel.
How is Dry Eye Diagnosed?
Dry eye disorders pose a challenging problem in diagnosis for physicians. Many different factors can contribute to dry eyes, and determining the cause may affect selection of the best treatment. Most important is listening carefully to a patient's history. Patients with dry eye are typically symptomatic for at least six months, and complain of a collection of symptoms which worsen as the day goes on:
Examination of the eyes is important to identify any eyelid abnormalities which may be present and contribute to symptoms of dry eye. Failing to correct eyelid problems often results in failure to relieve symptoms. A careful eye examination allows the physician to test the quality, quantity and stability of the tears and to look for irritation of the eye surface. Special dyes (colored eye drops) may reveal characteristic findings of dry eyes.
How is Dry Eye Treated?
The initial approach to treating dry eye syndrome is the use of topical tear substitutes (drops, gels or ointments). Many varieties are available, including thin, watery tear substitutes and thicker, more viscous eye drops. Several brands include electrolytes (salts) which may help heal the damaging effects of dry or "concentrated" tears on the surface of the eye. Ointments may be very soothing used at bedtime (to minimize the blurring produced). When symptoms persist despite the use of tear substitutes, closure of the tear ducts may be considered. This very valuable approach is similar to placing a plug in the drain in order to help a slow-running faucet fill a kitchen sink. Each eyelid has two "drains" or tear ducts near the bridge of the nose. Temporary plugs are available to test whether this treatment will offer relief of symptoms and are used before "permanent" (though removable) silicone plugs are inserted. This is done as a minor office procedure and can produce dramatic relief of dry eye symptoms. Strategies to increase the local humidity near the eyes may be very helpful for the more severe cases of dry eye. Plastic side shields attached to eyeglasses help prevent rapid evaporation of tears and may be very useful. In very severe cases, it may be necessary to suture the eyelids partially together at the corners to reduce the area exposed, also slowing loss of tears to evaporation.
What is Being Learned from Current Research on Dry Eye?
Current research has revealed much new information about what causes dry eye to develop. Hormonal factors are becoming understood, and will change how we treat dry eye. Within several years, hormone-containing tear substitutes may become available. Much work has been done on the use of medications which reduce inflammation on the eye surface. Eye drops containing cyclosporine have been studied and appear to be the first medication which actually treats the cause of dry eye, rather than simply treating the symptoms.