35.
Microplasmin-induced Vitreous Detachment
and the Role of Oxygenation
Mike T. Trese (Royal Oak)
Purpose: To determine if enzymatic induction of a posterior vitreous detachment (PVD) and/or
vitreous liquefaction affects 02 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 2 weeks post injection, vitreal oxygen concentration was measured using a
highly sensitive, platinum-based fluorophore 02 sensor. In addition, control and microplasmininjected
rats, guinea pigs, and cats were exposed to 100 % oxygen and vitreal 02 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 02 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 02 levels in any of the animal species (P>0.1). Upon
exposure to 100% oxygen by facemask, microplasmin injected animals showed a raid increase in vitreal oxygen levels compared
to hyaluronidase injected animals and controls, indicating that the presence of a PVD allows rapid 02 exchange within
the vitreous cavity. Similarly once 02 was discontinued, the 02 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 02 levels and increases
the rate of 02 exchange within the vitreous cavity.