Ultrastructure of the vitreoretinal interface following plasmin assisted vitrectomy

Aims-To investigate the ultrastructure of the vitreoretinal interface follo wing plasmin induced posterior vitreous detachment. Methods-Plasmin (1 or 2 U/0.1 ml) was injected into the vitreous cavity of 24 eyes of freshly slaughtered pigs. The 24 fellow eyes received calcium-fr ee and magnesium-free PBS and served as a control. After incubation at 37 d egreesC for 30 and 60 minutes, the globes were placed in fixative and hemis ected. Specimens for light, scanning, and transmission electron microscopy were obtained from the posterior pole, the equator, and the vitreous base u sing a corneal trephine. Results-All plasmin treated eyes showed posterior vitreous detachment. Howe ver, the inner limiting membrane (ILM) was covered by remnants of cortical vitreous at the posterior pole and at the equator. There was a direct corre lation between the concentration and exposure times of plasmin and the degr ee of vitreoretinal separation. Eyes exposed to 1 U plasmin for 30 minutes had a dense network of residual collagen fibrils while those exposed to 1 U plasmin for 60 minutes had only sparse collagen fibrils covering the ILM. Eyes treated with 2 U plasmin for 60 minutes had a smooth retinal surface, consistent with a bare ILM. At the vitreous base there was no vitreoretinal separation. In all control eyes the vitreous cortex was completely attache d to the retina. There was no evidence of retinal damage in any plasmin tre ated eye. Conclusion-Plasmin induces a cleavage between the vitreous cortex and the I LM without morphological changes to the retina. In contrast with previous r eports, plasmin produces a smooth retinal surface and additional surgery is not required in this experimental setting. The degree of vitreoretinal sep aration depends on the concentration and length of exposure to plasmin.