Dry Eye Syndrome

In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan.


Dry eyes, also known as dry eye disease (DED), dry eye syndrome, and keratoconjunctivitis sicca (KCS) are one of the most common reasons for a visit to an eye doctor. The definition of a dry eye according to the Tear Film and Ocular Surface Society Dry Eye Workshop II is: "Dry eye is a multifactorial disease of the ocular surface characterized by a loss of homeostasis of the tear film, and accompanied by ocular symptoms, in which tear film instability and hyperosmolarity, ocular surface inflammation and damage, and neurosensory abnormalities play etiologic roles."

The tear film is approximately 2 to 5 µm thick over the cornea and is composed of three main components. These components (lipid, aqueous, and mucin) are often described as layers, although this may be an oversimplification of the tear film milieu. The most superficial layer, the lipid layer, is produced by the meibomian glands of the eyelids and functions to reduce the evaporation of tears. The middle aqueous layer is the thickest component of the tear film and is produced by the lacrimal glands, located in the orbits, and the accessory lacrimal glands (glands of Krause and Wolfring) in the conjunctiva. The basal layer is composed of mucins, or glycoproteins, and is predominantly produced by conjunctival goblet cells. Mucins enhance the spread of the tear film over the corneal epithelium through the regulation of surface tension.

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