Which of the following layer of the tear film is the superficial layer which is in contact with air?
Layers of the tear film: The tear film is composed of three primary layers; The superficial lipid layer is a monomolecular film at the air-tear interface derived from meibomian glands. It is thought to retard evaporation and form a wateight seal when the lids are closed. The middle aqueous layer is elaborated by the major and minor lacrimal glands and contains water-soluble substances (salts and proteins). The deep mucinous layer is composed of glycoprotein and overlies the corneal and conjunctival epithelial cells. It is elaborated by goblet cells of the conjunctiva and also by the crypts of Henle and glands of Manz. Ref: Nijm L.M., Garcia-Ferrer F.J., Schwab I.R., Augsburger J.J., Correa Z.M. (2011). Chapter 5. Conjunctiva & Tears. In P. Riordan-Eva, E.T. Cunningham, Jr. (Eds), Vaughan & Asbury's General Ophthalmology, 18e.
Lipid layer
Aqueous layer
Mucinous layer
None of the above