AN INVESTIGATION OF ENZYME-ASSISTED VITRECTOMY
SHEHAB, SARAH ANNE
Doctor of Philosophy
Surgical vitreous removal (vitrectomy) is increasingly advocated to diminish the undesired consequences of retinal damage, which frequently arises from disease or injury to the vitreous. Current surgical techniques for vitrectomy use mechanical or ultrasonic devices that fragment and aspirate the vitreous from the eye. Because of the close proximity and attachment of the vitreous to the retina, this procedure itself incurs a high risk of inflicting retinal damage. Therefore, a less hazardous procedure for total vitrectomy is clinically desirable. This project primarily focuses on the use of enzymes as an adjunct to vitrectomy. Injected into the vitreous a few minutes prior to vitrectomy, the enzymes disrupt the structural integrity of the vitreous macromolecules and vitreo-retinal junction, making vitrectomy a less hazardous procedure. To investigate the effect of the enzymes on the vitreous, it was necessary to quantify changes in the rheological properties of the vitreous resulting from enzyme action. Three experimental schemes were devised for this purpose: firstly, a modified capillary viscometer was built in our laboratory. Secondly, vitrectomy instrumentation was used, and the time for total vitrectomy was measured in enzyme or control eyes. Lastly, a fluids rheometer was used to measure the elastic and viscous moduli and dynamic viscosity of enzyme or control eyes. The incidence of retinal damage caused by the enzymes was also estimated. The results showed that the most effective enzymes were chymopapain and chondroitinase ABC, which required short pretreatment times (20 minutes) and relatively low dose levels (10 and 0.6 mg/ml respectively). Both reduced the vitrectomy time by up to 61% of the controls and neither enzyme produced significant numbers of retinal detachments. Indeed, it was observed that chymopapain effected a clean detachment of the vitreous from the retina. Fluids rheometer experiments revealed that the mechanism by which these two enzymes assist vitrectomy is different.