Contraction of the vitreous or fibrovascular proliferations also may lead to retinal detachment. This may be limited to avulsion of a retinal vessel, sometimes accompanied by vitreous hemorrhage. Alternatively, a relatively thin fold of retina may become elevated, with only a narrow zone of retinal detachment adjacent to its base. In other cases retinal detachment may be more extensive, but the concave shape that is typical of traction detachment generally is maintained. If subretinal fluid from a tractional retinal detachment involves the macula, the prognosis for retention of acuity is grave (25). At times, what may appear clinically to be a shallow retinal detachment may be a schisislike splitting of the retina upon optical coherence tomography (26). Tractional retinoschisis of the retina results in severe retinal dysfunction of the involved region.

At times, small, apparently full-thickness retinal holes may be seen near the proliferations with traction; these sometimes, but not always, lead to rhegmatogenous detachment combined with the tractional components (a tractional–rhegmatogenous detachment). When such A detachment occurs, it tends to have a flat or convex anterior surface and be more extensive, even to the ora serrata. The occurrence and severity of retinal detachment are influenced by the timing and degree of shrinkage of the vitreous and fibrovascular proliferations and by the type, extent, and location of the vitreoretinal adhesions. New vessels with little accompanying fibrous tissue tend to produce less extensive vitreoretinal adhesions and less risk of retinal detachment, particularly when posterior vitreous detachment begins soon after the onset of neovascularization. At times, new vessels that extend for a considerable distance along the surface of the retina appear to be adherent to the retina only at their sites of origin and to the vitreous only near their distal ends. In this case the posterior vitreous surface can pull away before exerting traction on the retina. When new vessels are confined to the surface of the disc, vitreous detachment can reach completion without producing traction on the retina, since there are no vitreoretinal adhesions, but the vitreous remains tethered at the disc. Retinal detachment does not occur in such eyes, but recurrent vitreous hemorrhage from the new vessels is a risk.

Burned-Out Proliferative Diabetic Retinopathy

PDR may be considered to no longer be active when vitreous contraction has reached completion (i.e., when the vitreous has detached from all areas of the retina except those where vitreoretinal adhesions associated with new vessels prevent such detachment) (10, 18, 27, 28). Vitreous hemorrhages decrease in frequency and severity and may stop entirely, although many months may elapse before substantial vitreous clearing occurs. If retinal detachment is absent or only localized and the macula remains intact, visual acuity may be good. Frequently, however, dragging or distortion of the macula or longstanding macular edema leads to substantial reduction in vision. In many cases retinal detachment involves the entire posterior pole, with resultant severe loss of vision. Although spontaneous partial reattachment occasionally occurs, if the macula has been detached for months or years, usually no significant return of vision occurs. A marked reduction in the caliber of retinal vessels is characteristic of this stage. Previously dilated or beaded veins return to normal caliber or become narrower and often appear sheathed; fewer small venous branches are visible. Changes in the arterioles are often