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Christopher D. Riemann, Jianbo Zhou, David C. Buboltz; Vitreous Cutter Velocities: Dual Pneumatic Drive vs. Single Pneumatic Drive With Spring Return Probes. Invest. Ophthalmol. Vis. Sci. 2011;52(14):6132.
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© ARVO (1962-2015); The Authors (2016-present)
The blade velocity of a vitreous cutter affects tissue cutting shear rate, duty cycle, and flow rate through the cutter. All these parameters impact clinical cutting performance. A laboratory study using high speed videography of the cutter movement was conducted to investigate the cutter closing and opening velocities, and the durations of all phases of the cut cycle for two types of vitreous cutters - single pneumatic drive and spring return (SPDSR) and dual pneumatic drive (DPD) mechanisms.
High speed video of the cutter blade movement through the probe port was captured at 25000 frames per second. The SPDSR probes were run at 1500 and 2500 cpm. The DPD probes were run at 1500, 2500, and 5000 cpm with duty cycle biased open and also with duty cycle biased closed. Six each of 25, 23, and 20 gauge probes for both types were tested. The cutter movement was analyzed from the captured video frames to calculate the cutter closing and opening velocities and the durations of different phases of the cut cycle - opening, fully open, closing, and fully closed.
The closing and opening velocities for SPDSR probes at 2500 cpm and for DPD probes at 2500 and 5000 cpm are listed in the table. The measured duty cycle (percentage of time the port was fully open per cut cycle) at 2500 cpm was 26%, 38%, and 34% for the 25G, 23G, and 20G SPDSR probes, respectively; and 66%, 67%, and 62% for the 25G, 23G, and 20G DPD probes (core mode), respectively.
The DPD cutter closing and opening velocities are much higher than the SPDSR cutter creating a greater tissue cutting shear rate. For the DPD probes, the closing velocities are higher in smaller gauges, at higher cut rates, and with the duty cycle biased closed. Port open time was much longer for DPD probes (post biased open duty cycle) than for SPDSR probes. These results suggest that DPD vitreous cutter probes may have superior performance characteristics during actual vitrectomy surgery.
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