Vitrectomy Probe: The Affect of Cut Rate on Aspiration Flow Rate

Abstract

Abstract: : Purpose:To determine if direct control of Cut Rate can be utilized to indirectly control aspiration through a pneumatic Vitrectomy Probe. Methods:Pneumatic Vitrectomy Probes were operated at different cut rates utilizing fixed port–close and port–open timing cycles. The duration of dwell time between repeating port–close/port–open cycles was varied to create a range of cut rates. The period of time that the port was not obstructed by the cutter was measured for cut rates ranging from 100 to 2500 cpm and duty cycle was calculated. Infusion and vacuum levels were held fixed at 0 and 150 mmHg, respectively. Vitreous was not selected as the aspiration medium to reduce variation in results due to differences in vitreous characteristics. Clear fluid aspiration medium was utilized to enable detection of flow variations due to the phenomenon under study. The flow rate of the clear fluid was measured for a range of cut rates from 100 to 2500 cpm. Results:The cut–rate range of 100 to 2500 cpm resulted in duty cycles ranging from 97% to 28% and clear fluid flow rates ranging from 19 to 7 cc/min with 150 mmHg vacuum. Lower cut rates inversely resulted in higher duty cycles and higher flow rates, while higher cut rates resulted in a lower duty cycles and lower flow rates. The varying duty cycle of port obstruction by the cutter, during operation of the probe at various cut rates, varied the flow characteristics of the probe. Conclusions:It is generally understood that flow rate through a Vitrectomy Probe with a venturi suction system depends on the characteristics of the fluid being aspirated, the infusion pressure, and level of vacuum. This study shows that there is a fourth consideration when a pneumatic Vitrectomy Probe is used, cut rate. Direct control of cut rate can be utilized to indirectly control aspiration flow rates.

Keywords: vitreoretinal surgery • vitreous • retina