Physiology of Tear Production

Abstract

The tear film consists of three layers: an outer lipid layer, a middle aqueous layer, and an inner mucous layer. The numerous glands that surround the eye — various types of orbital glands — each contribute to the tear film. The meibomian glands and to a lesser extent the glands of Zeis and Moll secrete the lipids of the outer layer. The main lacrimal gland secretes the middle aqueous layer with an additional minor contribution from the accessory lacrimal glands (the glands of Kraus and Wolfring). The goblet cells and to some extent the crypts of Henle and the glands of Manz secrete the inner mucous layer. This chapter will focus mainly on two aspects of tear production: the neuroendocrine regulation of secretion from the orbital glands and the cellular mechanism of secretion.