Abstract
Purpose: :
To determine if induction of an enzymatic–assisted posterior vitreous detachment (PVD) and vitreous liquefaction affects O2 concentration in the vitreous cavity.
Methods: :
Either microplasmin (0.6 units) or hyaluronidase (25 units) was injected intravitreally into either guinea pigs or Brown Norway rats with the contralateral eye as a control. One week post injection, vitreal oxygen concentration was measured using a highly sensitive, platinum–based fluorophore O2 sensor (Oxford Optronix, Ltd.). In addition, control and microplasmin–injected animals were exposed to 100% oxygen by facemask, and vitreal O2 levels were measured over time. Scanning electron microscopy (SEM) was used to evaluate the vitreoretinal interface for the presence of a PVD.
Results: :
Intravitreal injection of microplasmin significantly increased vitreal O2 concentration in guinea pigs (4–fold, p<0.05) and rats (2–fold, p<0.005) as compared to control eyes. Intravitreal injection of PBS or hyaluronidase revealed similar vitreal O2 levels as compared to controls. When the normal, control guinea pig was exposed to 100% O2 the mid–vitreal levels of O2 steadily increased to 55 mm Hg over 20 minutes with a slow return to baseline when switched to room air. When exposed to 100% O2, microplasmin–treated eyes showed an accelerated increase in oxygen levels reaching 80 mm Hg in 2 minutes. The results suggest that an intact vitreous cavity may act as a buffer against elevated blood oxygen levels. SEM showed smooth retinal surfaces in microplasmin–injected eyes, indicating the presence of a PVD which was not present in control eyes.
Conclusions: :
Our results suggest that enzymatic–assisted PVD with microplasmin may increase vitreal O2 levels and increase O2 exchange within the vitreous cavity.
Keywords: vitreous • injection • oxidation/oxidative or free radical damage