Keratoconjunctivitis Sicca
Keratoconjunctivitis sicca (dry eye) is dryness of the conjunctiva and cornea.
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. This is the most common type found in postmenopausal women.
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 conjunctiva and cornea cannot be kept covered with a complete layer of tears during certain activities or in certain environments.
Rarely, aqueous tear deficient dry eyes may be a symptom of diseases such as rheumatoid arthritis, systemic lupus erythematosus, or Sjögren's syndrome.
Symptoms
Symptoms of dry eyes include irritation, burning, itching, a pulling sensation, pressure behind the eye, and a feeling like something is in the eye. 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 on a computer, driving, or watching television. Symptoms are also worse in dusty or smoky areas and dry environments, such as in airplanes or in shopping malls; on days with low humidity; and in areas where air conditioners (especially in the car), fans, or heaters are being used. Certain drugs can worsen symptoms, including isotretinoin, tranquilizers, diuretics, antihypertensives, oral contraceptives, and antihistamines. Symptoms improve 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 vision blurs with use, or the irritation is so severe that it is difficult to use the eyes. 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.
Diagnosis and Treatment
Although a doctor can usually diagnose dry eyes by the symptoms alone, a Schirmer test--in which a strip of filter paper is placed at the edge of the eyelid--can measure the amount of moisture bathing the eye. Doctors examine the eyes with a slit lamp (see Section 20, Chapter 225) to determine if the eye has been damaged.
Artificial tears (eye drops prepared with substances that simulate real tears) applied every few hours can generally control the problem. Avoiding dry, drafty environments and using humidifiers can help also. Minor surgery can be done to block the flow of tears into the nose, so that more tears are available to bathe the eyes. In people with very dry eyes, the eyelids may be partially sewn together to decrease tear evaporation.
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