Proliferative vitreoretinopathy

Proliferative vitreoretinopathy (PVR) is a disease that develops as a complication of rhegmatogenous retinal detachment. PVR occurs in about 8–10% of patients undergoing primary retinal detachment surgery and prevents the successful surgical repair of rhegmatogenous retinal detachment. PVR can be treated with surgery to reattach the detached retina but the visual outcome of the surgery is very poor.

PVR was originally referred to as massive vitreous retraction and then as massive periretinal proliferation. The name Proliferative vitreo retinopathy was provided in 1989 by the Silicone Oil Study group. The name is derived from proliferation (by the retinal pigment epithelial and glial cells) and vitreo retinopathy to include the tissues which are affected, namely the vitreous humor (or simply vitreous) and the retina.

During rhegmatogenous retinal detachment, fluid from the vitreous humor enters a retinal hole. The mechanisms by which retinal holes or tears form are not fully understood yet. The accumulation of fluid in the subretinal space and the tractional force of the vitreous on the retina result in rhegmatogenous retinal detachment. During this process the retinal cell layers come in contact with vitreous cytokines. These cytokines trigger the ability of the retinal pigmented epithelium (RPE) to proliferate and migrate. The process involved resembles fibrotic wound healing by the RPE cells. The RPE cells undergo epithelial-mesenchymal transition (EMT) and develop the ability to migrate out into the vitreous. During this process the RPE cell layer-neural retinal adhesion and RPE-ECM (extracellular matrix) adhesions are lost. The RPE cells lay down fibrotic membranes while they migrate and these membranes contract and pull at the retina. All these finally lead to secondary retinal detachment after primary retinal detachment surgery. A number of studies have also shown that arachidonic acid metabolic cascade (one of the major inflammatory cascades) is important in the development of PVR. COX-2 expression was found in human idiopathic epiretinal membranes.Phospholipase A2 and cyclooxygenase blocking reduced structural abnormalities of the rat retina in concanavalin model of PVR.

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