What is dry eye disease?
The tear film lubricates and nourishes the ocular surface and has three main components: lipid, aqueous, and mucin. The lipid layer, which is formed by the meibomian glands located in the tarsal plates of the eyelids, is an oily film that spreads onto the tear film and functions to slow evaporation of the aqueous component. The lacrimal glands produce the aqueous layer which contains dissolved carbohydrates, proteins, oxygen, and inorganic salts. The mucus layer, which is mainly formed by goblet cells in the conjunctiva, forms a foundation so the tear film can adhere to the eye. The tears evaporate from the ocular surface or enter the punctal openings where they are drained through canaliculi into the lacrimal sac and the nasolacrimal duct into the nose.
Dry eye disease is one of the most common problems treated by eye physicians. There are two forms of dry eye disease – aqueous deficient dry eye and evaporative dry eye. Evaporative dry eye is the leading cause of dry eye disease. Dry eye is a multifactorial disease of the tears and ocular surface that results in symptoms of discomfort, visual disturbance, and tear film instability with potential damage to the ocular surface. It is accompanied by increased osmolarity of the tear film and inflammation of the ocular surface.