Microplasmin-induced posterior vitreous detachment affects vitreous oxygen levels

Purpose: To determine if enzymatic induction of a posterior vitreous detachment (PVD) and/or vitreous liquefaction affects O-2 concentration in the vitreous cavity in animals with vascularized and avascular retinal circulations. Methods: Either microplasmin or hyaluronidase was injected intravitreally into guinea pigs (avascular retinal circulation), brown Norway rats (vascularized retinal circulation without fovea), or cats (vascularized retinal circulation with fovea) with the contralateral eye used as a control. One to O-2 weeks post injection, vitreal oxygen concentration was measured using a highly sensitive, platinum-based fluorophore O-2 sensor. In addition, control and microplasmin-injected rats, guinea pigs, and cats were exposed to 100% oxygen and vitreal O-2 levels were measured over time. Scanning electron microscopy (SEM) was used to evaluate the vitreoretinal interface for the presence of a PVD. Results: In animals with a vascularized retinal circulation (brown Norway rats and cats), intravitreal injection of microplasmin with induction of a PVD significantly increased baseline O-2 concentration in the vitreous cavity compared to hyaluronidase injected eyes and controls in rats (35, 25, and 23 mm Hg, P < 0.001 and P < 0.001, respectively) and cats (26, 18, and 16 mm Hg, P < 0.01 and P < 0.001, respectively). Interestingly, intravitreal injection of hyaluronidase (vitreous liquefaction without induction of a PVD) did not significantly increase vitreal O-2 levels in any of the animal species (P > 0.1). Upon exposure to 100% oxygen by facemask, microplasmin injected animals showed a rapid increase in vitreal oxygen levels compared to hyaluronidase injected animals and controls, indicating that the presence of a PVD allows rapid O-2 exchange within the vitreous cavity. Similarly, once O-2 was discontinued, the O-2 concentration decreased in a similarly rapid rate. SEM showed smooth retinal surfaces in microplasmin-injected cat eyes, indicating the presence of a PVD which was not present in hyaluronidase injected or control eyes. Conclusion: The results suggest that enzymatic-assisted PVD with microplasmin increases vitreal O-2 levels and increases the rate of O-2 exchange within the vitreous cavity.