A light and electron microscopic study of the healing of pars plana incisions in the rhesus monkey.

Pars plana incisions were made in 11 rhesus monkey eyes. Six animals had injections of 0.1 ml of blood into the vitreous cavity with a 25-gauge needle and five animals had vitrectomy through a 4-mm incision with a multifunction vitrectomy probe. Six to 13 years later the scars in the pars plana were found to consist of fibrous tissue and blood vessels which extended from the episclera into the vitreous. The intravitreous scar was shaped by the incarceration of vitreous strands in the internal aspect of the wounds. There were quantitative, but no qualitative differences between the two types of incision. The ultrastructural features were those of mature scar tissue: fibroblasts, adult collagen, uveal melanocytes, macrophages, myelinated and non-myelinated nerves, and capillaries with non-fenestrated endothelium. There were associated proliferative ciliary epithelial changes, but no evidence of ciliary epithelial metaplasia.