Vitreous Removal Rates and High–Speed Video Analysis of 25–Gauge Vitrectomy Cutters

Abstract

Purpose: : To compare the flow rates of guillotine, pneumatic, and electric cutters at various cut speeds and constant aspiration in porcine vitreous in–vitro. To use high–speed video analysis to measure the duty cycle and compare it to flow results.

Methods: : The 25–gauge Bausch and Lomb (St. Louis, MO) Lightning and 25–gauge Alcon (Fort Worth, TX) Accurus were operated at 550 mmHg aspiration and speeds of 600, 1000, and 1500 cuts per minute (CPM). During in–vitro cutting, the weight of the resulting vitreous was measured two times per second with an Ohaus (Pine Brook, NJ) balance, while real time data was recorded with National Instruments LabView (Austin, TX) and converted into flow rates. Sixteen trials were conducted with four pneumatic and four electric probes. The results were analyzed with SAS (Cary, NC) statistical software using a regression analysis, t–test, and confidence interval parameter. To analyze the duty cycle, high–speed video of the cutter tips in action was captured with a Dalsa (Waterloo, Ontario, Canada) 1M75 camera.

Results: : The rate of vitreous removal with the Bausch and Lomb Lightning cutter increased as speed increased. The Accurus, however, exhibited a lower flow rate with an increase in speed. The increasing and decreasing profiles of the two cutters intersected at 1000CPM, where the t–test yielded indistinguishable performance. At 1500 CPM, the Lightning demonstrated higher removal rates, while at 600 CPM, the Accurus was higher. At 1500 CPM, the mean removal rate of the Lightning cutter (0.0144 mL/s) was 235% higher than that of the Accurus (0.0061 mL/s). At 600 CPM, the mean of the Accurus (0.0134 mL/s) was 158% higher than that of the Lightning cutter (0.0084 mL/s). Confidence intervals and t–tests indicated statistical differences between the two cutters at these speeds. In addition, the high–speed camera revealed a constant duty cycle in the Bausch and Lomb Lightning and a reduced duty cycle as speed increased for the Alcon Accurus.

Conclusions: : With the Alcon Accurus, reduction in duty cycle corresponds with decreasing flow rates at higher cut speeds. In contract, the Bausch and Lomb Lightning had improved removal rates at higher cut speeds due to constant duty cycle.

Keywords: vitreoretinal surgery • vitreous • retina