Understanding Dry Eye Syndrome
The eyes are the only regularly exposed moist membrane on the body, putting them in a potentially dangerous situation because they can dry! Dry eyes may see poorly, and are more susceptible to infection and trauma. To keep the eyes moist, we blink 20-30 times per minute, constantly applying a fresh coat of tears and wiping away any particles of dirt, pollen, germs, etc. that might have landed. When we sleep, our eyelids close, preventing the tears from evaporating. Clearly an adequate tear film is important.
The cells lining the inside of the eyelids produce the tear film. The eyelids then distribute these products with each blink. When the eyelids are sick for any reason, patients often will develop a tear film insufficiency.
Although symptoms of tear deficiency become quickly noticeable by patients, they might not always recognize why they their eyes bother them. For instance, one of the signs of tear film insufficiency is frequent tearing! This is because when the baseline tear production is low, the eye gets irritated and signals special tear glands (the main lacrimal gland) normally reserved for crying to start producing tears. This gland can only produce large amounts of tears and so there is an apparent overproduction. Another symptom of tear film insufficiency is an itchy, gritty or burning sensation in the eyes. Finally, patients will complain of reduced vision because the tear film cannot perform its duty of smoothing the optical surfaces of the eye. Trauma, infection, or inflammations often cause the eyelids to become sick and prevent them from producing adequate tears. Often, mucous or ropy secretions will be seen on the eye.
Dry Eyes and Lid Problems
An eye can be dry even when the tears are normal. This occurs when the eyelids are malpositioned or deformed. This also can occur when the eyes blink with insufficient quality or frequency. Malpositions of the eye occur with aging, where the eye can evert (flip outward), a condition called ectropion, or invert (flip inward), a condition called entropion. Entropion can be especially dangerous because the eye can be traumatized by the eyelashes. Tumors, trauma, and inflammatory scarring can also cause these problems. When blinking is abnormally infrequent, it is usually the result of neurological disease. Alzheimer's disease and other causes of brain damage as well as diseases that decrease corneal sensitivity (herpes virus infections) all lessen the blink rate. When the blink rate is normal but the eye does not close sufficiently, a problem called exposure develops, and the eye can actually dry out. This is seen in neurological diseases that affect the part of the brain or the nerve that controls the muscles of eyelid closure. Ophthalmologists are specially trained to evaluate every part of a patient's eye-wetting mechanism to determine whether he suffers dry eye syndrome and to find the cause. They then use this information to tailor a treatment regimen for each patient's needs.
Treatment for Dry Eye
Although many different problems cause dry eye syndrome, the symptoms can often be lessened by topical lubrication. Topical lubricants vary in their thickness (viscosity) and chemical composition, but they all serve to keep the cornea moist. For short-term therapy, frequent applications of topical lubricants is acceptable to many patients. But this therapy can quickly become burdensome and is not without risks. Many lubricants can become allergenic and ultimately worsen the irritation in the eyes. The ophthalmologist will offer lubrication as a short term or temporizing measure but will strive to provide the patient with a more permanent solution to the problem. For example, if a patient's dry eye syndrome were secondary to allergies such as hay fever, the ophthalmologist would also prescribe topical anti-allergic medications. If a patient's dry eye syndrome were secondary to an immune-mediated inflammation that scarred the eyelids such as pemphigoid, the patient would instead be offered stronger anti-inflammatory agents and would also be directed to a rheumatologist, a physician who specializes in the treatment of such diseases.
Surgical therapy aims at correcting or at least lessening the disease process predisposing a patient to dry eye. For example, if a patient has lost the ability to blink his eye because of a neurological condition, the ophthalmologist may offer a temporary tarsorraphy, a procedure in which the eyelid is partially or completely closed so that the cornea can be protected until the return of the ability of the eyelid to blink. If a patient has disease of the lacrimal glands preventing sufficient tear production, the ophthalmologist might close the lacrimal puncta, four tiny holes in the eyelids that drain away the tears, permitting the tear film to remain on the eye longer. Or if a patient has an everted eyelid that does not hold the tear film in its normal place against the eye, the ophthalmologist can perform an operation to reposition the eyelid to a more normal position, a procedure called an ectropion repair. In any case, patients should know that while dry is a terribly common, unpleasant and under-diagnosed disease, temporary and permanent therapies are available.
The cornea is the main victim of dry eye. Ultimately, the chronic irritation will cause the cornea to develop erosions, or even infected ulcers. Ulcers can actually involve the entire cornea thickness and melt a hole in the cornea, a condition known as a perforated globe. Because the contents of the inside of the eye are under pressure, the inside of the eye can be pushed out through this hole. Even if the cornea is treated for erosions and ulcers, it will eventually scar and deform, losing the ability to focus light well and leaving a patient with uncorrectably poor vision. When this occurs, the best option for improvement of sight is a corneal transplant. In this procedure, the patient's diseased cornea is removed and a new human cornea is transplanted in its place. This cornea, like any other cadaverically derived tissue, was donated by some individual who wanted to give of themselves even after passing away. Ophthalmologists recognize and respect the generosity and rarity of this type of gift, and treat the transplanted corneas with extreme care. For this reason, they are very careful when deciding to whom they offer a corneal transplant, in an attempt to ensure that the new cornea will not only benefit a patient but will also last.
Restasis®
Restasis® is a relatively new prescription eyedrop that promotes increased tear production and a better quality tear to be produced by the lacrimal, or tear gland, in your own eye. This can eliminate or greatly reduce the need for over-the-counter artificial tears. However, it does have to be used chronically and is fairly expensive if you have no coverage for medicine.
Punctal Plugs
Punctal plugs are tiny plugs that are made of collagen (temporary) or silicone (permanent) which are designed to occlude the opening in the eyelid, called the punctum, from which tears drain. These plugs simply act as a mechanical barrier and help to keep tears on the eye longer, which can help soothe the eye. They can be placed in the eyelids in the office and can provide years of symptomatic improvement.
