Pars planitis.

We have studied seven eyes from six patients with longstanding pars planitis. Two eyes were phthisical. The remaining five eyes from four patients showed similar findings and included retinal phlebitis, disc and macular oedema, and the presence of a 'snowbank' over the inferior peripheral retina and pars plana. The snowbank consisted of posteriorly detached and collapsed vitreous in which cellular proliferation from the retina with non-pigmented ciliary epithelium was present. Electron microscopy showed the presence of fibrous astrocytes and collagen in two eyes. Retinal neovascularization extended into the snowbank in one case. We have also studied vitreous and preretinal membranes and a portion of a snowbank obtained by pars plana vitrectomy from two eyes of two young patients with active pars planitis. The snowbank and preretinal membranes contained fibrous astrocytes and new collagen and the vitreous snowballs consisted of granulomatous inflammation.