Proliferative vitreoretinopathy (PVR) is the leading cause of failure of retinal detachment surgery. In this disorder, contractile cellular membranes form within the vitreous cavity. Retinal pigment epithelial (RPE) cells are an early and important component of these membranes. Contraction is mediated by cellular events and this contraction results in the formation of traction retinal detachments. Using the techniques of time-lapse cinemicrography, the authors studied the interaction of single RPE cells with individual strands of collagen. RPE cells pull the collagen fibers toward them using alternating extension and retraction of their lamellipodia. (The mechanism can be likened to sailors pulling in sheets of a sal in a hand-over-hand manner.) The collagen is not engulfed by the cell, but instead is piled up in a small bundle adjacent to the cell. Using this mechanism, each cell can reel in several times its length of collagen in 1 hour. In this manner, a small number of RPE cells may be able to collapse the vitreous gel and exert tractional forces.