Introduction: Tear production, distribution, and clearance are regulated by the Lacrimal Function Unit that consists of the main and accessory lacrimal glands, the meibomian glands, the conjunctiva, eyelids, and blink apparatus. Tear dysfunction develops when one or more of these components is no longer able to maintain a stable tear film. Tear dysfunction is one of the most common eye conditions with a reported prevalence of 6 to 43 million in the United States, depending on the diagnostic criteria. Tear dysfunction causes eye irritation and visual symptoms, including photophobia and blurred and fluctuating vision. Tear dysfunction can cause pathologic changes to the ocular surface epithelium with disruption of corneal epithelial barrier function and loss of mucus secreting conjunctival goblet cells. It may also decrease quality of life and in the most severe cases, it can cause functional and occupational disability. Indeed, the impact of dry eye on quality of life was rated to be equivalent to unstable angina using utility assessments.
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