High osmolarity effect of intravitreal plasmin enzyme on rabbit retina

We conducted a study of the effect of intravitreal plasmin on retinal thickness in rabbits. Forty rabbit eyes were injected with 0.4, 1, 2, and 5 IU of plasmin (8 eyes/group). The same volume of BSS-plus(®) was injected in control eyes. Four eyes in each group underwent vitrectomy 60 minutes after the injections. The retinal thickness was measured in optical coherence tomographic (OCT) images before, 30 minutes, and 1 week after the injection. To study the effect of hyperosmolarity, 4 eyes received an injection of mannitol solution whose osmolarity was the same as the plasmin solutions. Thirty minutes after the plasmin injection, 4 eyes developed a serous retinal detachment (SRD). The mean retinal thickness including SRD was increased at 30 minutes in a dose-dependent way. The increase in eyes with 5 IU of plasmin was significantly greater than that in eyes with BSS-Plus(®) or 0.4 IU of plasmin (P = 0.0266, P = 0.0371, respectively). One week after the injection, SRD disappeared, and the mean retinal thickness decreased. The eyes injected with mannitol, the same osmolarity of 1, 2, 5 IU of plasmin, developed SRD at 30 minutes, and it disappeared after 1 week in all eyes. The results of this study demonstrated that an intravitreal injection of plasmin increases the retinal thickness in a dose-dependent way in rabbit eyes. The results with mannitol suggest that the increase in retinal thickness following plasmin is most likely caused by the hyperosmolarity of plasmin solution.