[Posterior hyaloid membrane as structural base of growth of neovascular tissue in proliferative diabetic retinopathy].

Morphologic study of 38 specimens of epiretinal membranes obtained during transciliary vitrectomy in 26 patients with type I diabetes mellitus and 12 with type II diabetes with proliferative diabetic retinopathy of different stages was carried out. In proliferative diabetic retinopathy, new vessels grow mainly along the posterior (retinal) surface of the posterior hyaloid membrane. Sometimes, if there are defects in the posterior hyaloid membrane, proliferative tissue stratifies it and appears on the anterior (hyaloid) surface. We observed no growth of new vessels outside the posterior hyaloid membrane. The impossibility of clinical and mechanical separation of the posterior hyaloid membrane and tumor tissue permits us to regard the stages of proliferative process in diabetic retinopathy as stages in the alteration of the posterior hyaloid membrane proper. Five variants in the structure of proliferative tissue can be distinguished in diabetic retinopathy; we consider that these variants are stages in its development: 1) glial--with predominance of cell-free or hypocellular glial tissue; 2) glial vascular--with growth of thin-wall vessels into glial tissue; 3) glial vascular fibrous--with growth of porous fibrovascular membrane in glial tissue; 4) fibrovascular--with predominance of fibrovascular tissue; and 5) fibrous (cicatricial) hypocellular compact connective tissue with just few vessels or none at all. Reduction of new vessels, involution of proliferative tissue, and development of traction detachment of the retina are associated with the beginning of fibrous proliferation.