eye disorders
Keratoconjunctivitis Sicca
Causes of Keratoconjunctivitis Sicca
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 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.Isotretinoinand antiandrogens (drugs that inhibit male hormones) are just some of the drugs that can contribute to this type of dry eye. 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 (PD) ). Some antipsychotics, adrenergic agonists (certain antihypertensives), and botulinum toxin injections can all aggravate dry eye due to nocturnal lagophthalmos. 