Dry eye is a frequent cause of eye irritation. A lack of a single diagnostic test for the condition limits the available epidemiologic data. One study estimated the prevalence of dry eye in the U.S. population age 65 and older at 14.6%, which is approximately
4.3 million Americans.
FIGURE 63-4. Amsler's grid distortions in the lines of the grid may be caused by subtle changes in central vision due to fluid in the subretinal space. This is the Amsler's grid as it appears to someone with normal vision. (From the National Eye Institute, National Institutes of Health Ref. No. EC03. Accessed online at: http://www.nei.nih.gov/photo/)
The risk factors for dry eye are listed in Table 63-10. Of interest, the use of caffeine is associated with a decreased risk of dry eye. Dry eye that is left untreated can
cause loss of vision or other morbidities over time. PATHOPHYSIOLOGY
The ocular surface and the tear-secreting glands of the eye function as an integrated unit. This unit refreshes the tear supply and clears away used tears. An autonomic neural reflex loop stimulates secretion of tear fluid and proteins by the lacrimal glands. The sensitivity of the ocular surface decreases with the decrease of aqueous tear production and tear clearance. This results in a decrease in sensory-stimulated reflex tear-
ing which exacerbates dry eye. ' Over time, wearing contact lenses also desensit-
izes the cornea by constant stimulation.
Table 63-10 Risk Factors for Dry Eye
Estrogen replacement therapy
Table 63-11 Associated Conditions That Cause or Worsen Dry Eye
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