(Dry Eye; Keratitis Sicca)
(See also Introduction to Corneal Disorders.)
Dry eyes may be due to inadequate tear production (aqueous tear-deficient dry eyes). With this type of dry eyes, the tear gland (lacrimal gland) does not produce enough tears to keep the entire conjunctiva and cornea covered by a complete layer of tears. (See figure Structures That Protect the Eye.) This is the most common type among postmenopausal women. Dry eyes are common in Sjögren syndrome. Rarely, aqueous tear-deficient dry eyes may be a symptom of diseases such as rheumatoid arthritis or systemic lupus erythematosus (lupus).
Dry eyes may also be due to an abnormality of tear composition that results in rapid evaporation of the tears (evaporative dry eyes). Although the tear gland produces a sufficient amount of tears, the rate of evaporation is so rapid that the entire surface of the eye cannot be kept covered with a complete layer of tears during certain activities or in certain environments.
Drying can also result from the eyes being partly open for periods of time at night (nocturnal lagophthalmos) or from an insufficient rate of blinking (as can occur in Parkinson disease).
Symptoms of dry eyes include irritation, burning, itching, a pulling sensation, pressure behind the eye, and grittiness or a feeling as if something is in the eye (foreign body sensation). Damage to the surface of the eye increases discomfort and sensitivity to bright light. Symptoms are worsened by
Activities in which the rate of blinking is reduced, specifically those that involve prolonged use of the eyes, such as reading, working at a computer, driving, or watching television
Windy, dusty, or smoky areas and dry environments, such as in airplanes or in shopping malls; areas with low humidity; and areas where air conditioners (especially in the car), fans, or heaters are being used
The use of certain drugs, including isotretinoin and some tranquilizers, diuretics, antihypertensives, oral contraceptives, and antihistamines, and other drugs with anticholinergic effects
Symptoms lessen during cool, rainy, or foggy weather and in humid places, such as in the shower.
Even with the most severe dry eyes, it is rare that vision is lost. However, people sometimes feel that their blurred vision or eye irritation is so severe, frequent, and prolonged that it is difficult to function normally. In some people with severe dryness, the surface of the cornea can thicken, or ulcers and scars can develop. Occasionally, blood vessels can grow across the cornea. Scarring and blood vessel growth can impair vision.
Doctors diagnose dry eyes by the symptoms and appearance of the eyes and by doing some tests.
Doctors examine the eyes with a slit lamp (an instrument that enables a doctor to examine the eye under high magnification) to determine whether the eye has been damaged. During the examination, the doctor may apply eye drops that contain a yellow-green dye called fluorescein. The fluorescein temporarily stains damaged areas of the cornea, making it possible to see damaged areas that are not otherwise visible.
The Schirmer test—in which a strip of filter paper is placed at the edge of the eyelid—is used to measure the amount of tears produced during the 5-minute test.
They may also measure how long it takes for the eye to become dry when the person stares (called the tear breakup time).
Artificial tears applied every few hours can generally control the problem. Artificial tears are eye drops prepared with substances that simulate real tears and help keep the eyes coated with moisture. Lubricating ointments applied before bed last longer than artificial tears and help prevent dryness in the morning. Such ointments are not usually used during the day because they may blur vision. Some doctors may recommend omega-3 fatty acid dietary supplements to improve the oil film of the eye.
Eye drops that contain cyclosporine can decrease the inflammation associated with dryness. These drops sting and take months before an effect is noticed. Inflammation can lessen significantly, although the drops work only in a fraction of people. Avoiding dry, drafty environments and smoke and using humidifiers can also help.
An ophthalmologist (a medical doctor who specializes in the evaluation and treatment―surgical and nonsurgical―of eye disorders) can do a minor in-office procedure to help people with dry eyes. During the procedure, an ophthalmologist inserts plugs into the puncta (the small openings at the inner corners of the eyelids near the nose) to keep tears from leaving the eye by blocking the flow of tears off of the eye surface, through the tear duct, and into the nose. This way more tears are available for longer to bathe the eyes. In people with extremely dry eyes, the eyelids may be partially sewn together to decrease tear evaporation.
A device that improves dry eyes symptoms by electrically stimulating tear production through a soft-tipped probe placed into the nose several times a day can also be tried, if other methods for treating aqueous deficient dry eye were insufficient.
If a person has blepharitis, it is treated with measures such as warm compresses, massage and heating devices, eyelid scrubs, and sometimes oral antibiotics.
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