The International Workshop on Meibomian Gland Dysfunction: Report of the Subcommittee on Anatomy, Physiology, and Pathophysiology of the Meibomian Gland

Abstract

T he tarsal glands of Meibom (glandulae tarsales) are large sebaceous glands located in the eyelids and, unlike those of the skin, are unassociated with hairs.According to Duke-Elder and Wyler, 1 they were first mentioned by Galenus in 200 AD and later, in 1666, they were described in more detail by the German physician and anatomist Heinrich Meibom, after whom they are named.Lipids produced by the meibomian glands are the main component of the superficial lipid layer of the tear film that protects it against evaporation of the aqueous phase and is believed also to stabilize the tear film by lowering surface tension. 2 Hence, meibomian lipids are essential for the maintenance of ocular surface health and integrity.Although they share certain principal characteristics with ordinary sebaceous glands, they have several distinct differences in anatomy, location, secretory regulation, composition of their secretory product, and function.Functional disorders of the meibomian glands, referred to today as meibomian gland dysfunction (MGD), 3 are increasingly recognized as a discrete disease entity.4 -8 In patients with dry eye disease, alterations in the lipid phase that point to MGD are reportedly more frequent than isolated alterations in the aqueous phase.In a study by Heiligenhaus et al., 9 a lipid deficiency occurred in 76.7% of dry eye patients compared with only 11.1% of those with isolated alterations of the aqueous phase.This result is in line with the observations by Shimazaki et al. 10 of a prevalence of MGD in the absolute majority of eyes with ocular discomfort defined as dry eye symptoms.These observations noted that 64.6% of all such eyes and 74.5% of those excluding a deficiency of aqueous tear secretion were found to have obstructive MGD, or a loss of glandular tissue, or both.10 Horwath-Winter et al. 11 reported MGD in 78% of dry eye patients or, if only non-Sjo ¨gren patients are considered, in 87% compared with 13% with isolated aque-ous tear deficiency.It may thus be accepted that MGD is important, conceivably underestimated, and possibly the most frequent cause of dry eye disease due to increased evaporation of the aqueous tears.5,9 -12 After some excellent reviews of MGD 4,7,8,13,14 in the past, many new findings have been reported in recent years, and other questions remain to be identified and resolved.A sound understanding of meibomian gland structure and function and its role in the functional anatomy of the ocular surface 15 is needed, to understand the contribution of the meibomian glands to dysfunction and disease.Herein, we seek to provide a comprehensive review of physiological and pathophysiological aspects of the meibomian glands. HEINRICH MEIBOMHeinrich Meibom the younger (1638 -1700; Fig. 1) 16 came from a scholarly family.He was the son of the physician Johann Heinrich Meibom and the grandson of the German historian and poet Heinrich Meibom the elder (1555-1625), 17 who was professor of history and poetry at the University of Helmstedt in Germany.Heinrich Meibom the younger was born on June 29, 1638, in Lu ¨beck, Germany, and later traveled around in Europe and received a cosmopolitan education.In a short article 18 that commemorated the 300th anniversary of his birth in 1938, the British Medical Journal characterized him as follows: "Like so many of his contemporaries, he was indeed a child of Apollo, god of culture, poetry, rhetoric, and healing.While still a medical student (he became MD at Angers in 1663) he was appointed to, and in 1664 took up, the professorship of medicine in the University of Helmstadt.Fourteen years later he accepted the additional chairs of history and of poetry.He further showed his versatility by straying into the pleasant fields of archaeology, philology, and philosophy, and all his life he was an insatiate traveller."Apparently a man of many talents, in 1666, shortly after receiving the chair of medicine, Heinrich Meibom published the first detailed description, including a drawing, of the oil glands inside the tarsus of the eyelid, that later were named the meibomian glands.His description appeared as a book with the title De Vasis Palpebrarum Novis Epistola.19 This early drawing showed basic characteristics of the glands, such as multiple single gland streaks along the extension of the tarsus with openings onto the lid margin, similar to but not as detailed as another much later and more well-known drawing (Fig. 2).