Purpose: To investigate the efficacy and safety of intravitreal injection of plasmin in producing posterior vitreous detachment (PVD), and the possible role of plasmin in degrading adhesion glycoproteins of the internal limiting membrane (ILM).
Methods: A total of 20 young human cadaver eyes were randomized into four groups. Groups 1, 2, and 3 were injected with 1, 2, and 3 U of human plasmin, respectively, and group 1 was injected with 0.1 ml balanced salt solution as control. Optical and transmission electron microscopy were used to examine the ultrastructure of the vitreoretinal interface. The amounts of fibronectin (FN) and laminin (LN) in the ILM were determined using electron-immunocytochemical techniques. The survival of retinal cells was evaluated using flow cytometry. Analysis of variance (ANOVA) and the Tukey test were used for statistical analysis.
Results: Microscopy showed that plasmin, especially in group 4, cleaved the attachment of the vitreous collagen fibrils to the ILM. There was no evidence of damage to the inner retina except some post-mortem lytic changes. The amounts of LN and FN in the ILM were decreased following injection of plasmin. There were statistically significant differences in the amounts of FN in groups 3 and 4 compared to the control group (P<0.05), and in the amount of LN in group 4 (P<0.05). Retinal cell viability was similar in both treated and control eyes.
Conclusion: Human plasmin can disrupt the attachment of the posterior hyaloid to the ILM without producing morphological changes or acute toxicity of the inner retina of the human eye. PVD can be induced completely by injection of 3 U plasmin. The enzyme may be useful for removing the cortical vitreous during vitreous surgery.