Low tension glaucoma (LTG) is a condition consisting of typical gluacomatous disc and field changes, an open angle and pressures within the statisticaly normal range. The controversy surrounding low tension glaucoma pertains not only to the definition and characteristics of the entity itself, but to the fundamental questions it raises regarding the causal relationship between intraocular pressure and disc and field changes. This review of LTG is based on material from three major sources: Sjögren's review from 1857 to 1946; the author's review of the world literature from 1947 through 1979; and an analysis of 32 of the author's cases. 767 cases from clinic and private practice and 241 cases from defined populations are considered. Definitions, incidence, characteristics, differential diagnosis and management of LTG are discussed, as are its relationship to primary open angle glaucoma and its possible association with various other entities. Pathogenesis and possible mechanisms are also explored.