Performance analysis of new-generation vitreous cutters.

BACKGROUND

Despite their clinical advantages, smaller-diameter vitrectomy systems pose significant challenges in vitreous removal. The percentage of time the vitreous cutter port is open while cutting (duty cycle) is one of the primary factors that affect flow. Herein, we examine the effect of duty cycle on the flow performance of new-generation cutters relative to current instrumentation.

METHODS

Performance of 25-gauge (ga) and 20-ga new-generation spring-return pneumatic cutters (n = 24 and n = 28 respectively) was analyzed relative to current-generation cutters, across their specified cut-speed range under clinical vacuum pressures of 500 mmHg (25-ga) and 200 mmHg (20-ga). A precision balance measured mass of water or porcine vitreous removed from a vial by a cutter; this was recorded in real-time and converted to flow rates. Frame-by-frame analysis of high-speed video was used to determine duty cycle. Data was analyzed using linear regression and the t-test.

RESULTS

Compared with the current-generation, the new-generation cutters exhibit increasingly greater water flow rates at higher cut speeds (P < 0.001). Vitreous flow rates of the new-generation cutters are relatively constant as cut speed increases, and are significantly greater than those of the current-generation cutters at cut speeds of 1500 cuts per minute (CPM) or higher (P < 0.001). The new-generation 25-ga cutter exhibits greater vitreous flow rates at higher cut speeds than the current-generation 20-ga cutter: at 2000 and 2500 CPM, the new 25-ga cutter has 1.45 and 11.88 times the vitreous flow rate of the current 20-ga cutter (P < 0.001) respectively. Duty cycles of the new-generation cutters are significantly higher than those of the current-generation at all cut speeds (P < 0.001).

CONCLUSIONS

Although a number of factors influence flow, the high and relatively constant vitreous flow rates of the new-generation cutters are most likely due to their maintenance of high duty cycle as cut speed increases. The findings illustrate that in optimizing duty cycle, the vitreous flow efficiency of smaller-diameter cutters can match or exceed that of larger diameter cutters.