eye disorders
Keratoconjunctivitis Sicca
Etiology of Keratoconjunctivitis Sicca
The conjunctival and corneal surface epithelial cells need to be hydrated. If there is interruption of a continuous, unbroken layer of tears over the exposed surface, desiccation of surface cells leads to tissue damage and inflammation. There are 2 main types: Aqueous tear-deficient keratoconjunctivitis sicca is caused by insufficient coverage of the ocular surface by tears due to inadequate tear volume. Evaporative keratoconjunctivitis sicca (more common) is caused by insufficient coverage of the ocular surface by tears due to accelerated tear evaporation resulting from poor tear quality. Aqueous tear-deficient keratoconjunctivitis sicca is most commonly an isolated idiopathic condition in postmenopausal women. It is also commonly part of Sjögren Syndrome , Evaporative keratoconjunctivitis sicca is caused by loss of the tear film due to abnormally rapid evaporation caused by an inadequate oil layer on the surface of the aqueous layer of tears. Symptoms may result from abnormal oil quality (ie, meibomian gland dysfunction) or a degraded normal oil layer (ie, seborrheic blepharitis). Patients frequently have Rosacea . Drying can also result from exposure due to inadequate eye closure at night (nocturnal lagophthalmos or Bell or Facial Nerve Palsy ) or from inadequate frequency of reapplication of tears to the cornea due to an insufficient blink rate (eg, in Systemic drugs can cause or aggravate dry eyes. Different classes of drugs contribute to different types of dry eye, as in the following examples: Aqueous tear-deficient dry eyes: Diuretics, anticholinergics, antidepressants, beta-blockers, decongestants, oral contraceptives Evaporative dry eyes:Isotretinoin, antiandrogens Dry eyes due to poor eyelid closure: Major antipsychotics, adrenergic agonists, botulinum toxin injections 