The term retinitis proliferans is purely descriptive and applies to a variety of pathologic conditions due to different causes. The expression retinitis designates a pathologic process in the retina, not necessarily of an inflammatory nature, and the adjective proliferans indicates the plastic character of the lesions. Clinical and histologic studies of eyes during the earlier stages of proliferating retinitis reveal that there are two principles involved in the production of this condition, leading to two essentially different types of retinitis proliferans: type 1, in which the formation of connective tissue precedes the formation of new blood vessels, and type 2, in which there is a primary formation of new vessels with secondary production of a scaffolding of delicate connective tissue. In type 1 exudation or hemorrhage from the retina into the vitreous, caused by inflammatory or traumatic alterations of the retinal vessels, is the primary event, and