Recombinant tissue plasminogen activator injected into the vitreous cavity may penetrate the retinal veins of a porcine model of vascular occlusion.

AIM: To determine if recombinant tissue plasminogen activator (rtPA) injected into the vitreous cavity can penetrate the retinal vessels of porcine eyes with or without vascular occlusion. METHODS: Eight eyes (group I) of four pigs underwent clamping of the optic nerve flush with the globe for 90 minutes. One hour after reperfusion, one eye of each pig was injected with 75 microg of rtPA, and the fellow eye was injected with balanced salt solution (BSS). Eyes were processed for immunohistochemistry. Four additional eyes (group II) of two pigs were subjected to the same injections, but without optic nerve clamping. RESULTS: After reperfusion, the clinical picture was similar to that of a central retinal vein occlusion. Immunoperoxidase staining showed rtPA only in the retinal veins but not the retinal arteries in all eyes injected with rtPA in both groups I and II. Those eyes also showed intense rtPA staining at the level of the internal limiting membrane (ILM). No staining was seen at the level of the ILM or inside the retinal vessels in the BSS injected eyes. Immunofluorescence staining showed intense staining at the level of the ILM, but not inside the retinal vessels in the rtPA-injected eyes. CONCLUSIONS: rtPA may penetrate the retinal veins, but not the arteries of porcine eyes with and without vascular occlusion. The ILM may play a part in preventing rtPA penetration.

Dispase facilitates posterior vitreous detachment during vitrectomy in young pigs.

PURPOSE: To evaluate the role of intravitreal dispase in conjunction with pars plana vitrectomy to facilitate the creation of a posterior vitreous detachment (PVD) in young pig eyes. METHODS: Twenty-four eyes of 24 animals were randomized to receive an intravitreal injection of dispase (50 microg/0.05 mL) or phosphate buffered saline (PBS) immediately after core vitrectomy and before attempted creation of a posterior cortical vitreous detachment. Following a 15-minute waiting period, surgical creation of a posterior vitreous separation was attempted by aspiration of the posterior vitreous immediately adjacent to the optic disk. Eyes were evaluated postoperatively by clinical examination (1, 4, and 8 weeks) and electroretinography (4 and 8 weeks), after which they were enucleated for light, scanning, and transmission electron microscopy. RESULTS: Based on intraoperative findings and postoperative scanning electron microscopy, eyes receiving intravitreal dispase exhibited a higher incidence of PVD compared to eyes receiving PBS (P = 0.029). Electroretinographic responses recorded at postoperative weeks 4 and 8 were similar in both dispase and PBS eyes compared to the unoperated fellow eyes. Clinical examinations, including indirect ophthalmoscopy, were indistinguishable between the PBS eyes and 11 of 12 eyes in the dispase group. Light and transmission electron microscopy demonstrated no differences in the retina between the dispase eyes and the PBS operated controls. CONCLUSION: Dispase is a useful adjunct in facilitating surgical creation of a PVDin young pig eyes.