From: The International Workshop on Meibomian Gland Dysfunction: Report of the Subcommittee on Anatomy, Physiology, and Pathophysiology of the Meibomian Gland Invest. Ophthalmol. Vis. Sci.. 2011;52(4):1938-1978. doi:10.1167/iovs.10-6997c Figure Legend: Driving forces for the delivery of meibomian oil onto the lid margin and tear film. A schematic drawing of a single meibomian gland inside the connective tissue of the tarsus at the posterior lid margin. The driving forces that result in the eventual delivery of meibomian oil (meibum) onto the lid margin and tear film are (1) the continuous secretion of meibum by the secretory acini, which generates a secretory pressure that pushes the meibum (yellow arrows) into the ductal system and further toward the orifice and (2) the mechanical muscular action by muscle fibers (red dots) of the pretarsal orbicularis muscle (M. orbicularis), located on the outside of the tarsus, and of the marginal muscle of Riolan (M. Riolan), which encircles the terminal part of the meibomian gland. During a blink, these muscles may exert a compression (red arrows) of the meibomian gland that drives the oil out of the orifice into the marginal lipid reservoir, where it eventually constitutes the tear film lipid layer (TFLL), as observed clinically [compare with Figs. 3, 7, and 18]. Reprinted from Knop E, Knop N, Schirra F. [Meibomian glands. Part II: physiology, characteristics, distribution and function of meibomian oil] Meibom-Drüsen Teil II: Physiologie, Eigenschaften, Verteilung und Funktion des Meibom-Öls. Ophthalmologe. 2009;106:884–892, with the kind permission of Springer Science and Business Media. Date of download: 11/10/2017 The Association for Research in Vision and Ophthalmology Copyright © 2017. All rights reserved.