Retinal thickness changes in rabbit eyes after intravitreal plasmin injection

Abstract

Abstract: : Purpose: To study the effect of intravitreal plasmin on retinal thickness in rabbits. Methods:Intravitreal injection of 0.4, 1, 2, and 5IU of plasmin, or BSS–plus^® (8/group) was performed in 20 pigmented rabbits (40 eyes). Four eyes in each group underwent vitrectomy 60 minutes after the injection. The retinal thickness, from the retinal pigment epithelium to the internal limiting membrane, was measured by optical coherence tomography (OCT) before, and 30 minutes and 1 week after the injection. Four other rabbits were used to determine the effect of hyperosmolarity on retina. One eye of each rabbit underwent injection of 0.1 ml of mannitol solution, which was adjusted to the same osmolarity (390, 500, 690, 1250 mOsm) as the plasmin solutions. OCT images were obtained 2 hours and 1 week after the injection of mannitol. Results: Four eyes injected with plasmin (1 with 1 IU, 1 with 2 IU, 2 with 5 IU) developed a serous retinal detachment (SRD) 30 minutes after the plasmin. The mean retinal thickness 30 minutes after plasmin injection increased proportionally to the concentration of plasmin, and the increase in eyes with 5 IU of plasmin was significantly greater than that in eyes with BSS–plus^® and 0.4 IU of plasmin (P=0.0266, P=0.0371, respectively). One week after the plasmin injection, the SRD disappeared regardless of whether vitrectomy was performed or not, and the mean retinal thickness decreased. The eyes injected with 500, 690, and 1250 mOsm of mannitol developed SRD at 2 hours, which disappeared after 1 week. Conclusions: Plasmin increased the retinal thickness in rabbits in proportion to the concentration of plasmin. The mannitol experiments suggested that the effect of plasmin may be caused by the hyperosmolarity of the plasmin solution.

Keywords: proteolysis • pharmacology • vitreoretinal surgery