Abstract
Purpose: :
In order to maximize surgical efficiency and optimize vitrectomy system control parameters, it is important to fully understand flow dynamics of vitreous during vitrectomy. It was previously reported that vitreous flow rates of 20, 23, and 25 gauge dual-pneumatic drive vitrectomy probes achieved maximum aspiration at 5000 cpm. This study extends the previous study by investigating the relationship between porcine vitreous flow rates, probe gauge, duty cycle, and vacuum at high speed cut rates of up to 7500 cpm.
Methods: :
The CONSTELLATION® Vision System (Alcon Laboratories, Inc.) was tested with UltraVit® vitrectomy probes at 250, 450, and 650 mmHg of vacuum. Three probe gauges were evaluated (23, 25+™ , and 27+™ gauge) at three duty cycle modes offered with the surgical platform: "core" (port biased open), "50/50" (50% port open time), and "shave" (port biased closed). Flow rates were calculated by measuring the change in weight over time of porcine eyes placed on an electronic scale during open sky vitrectomy.
Results: :
In the biased-open mode at 250 and 450 mmHg vacuum, vitreous flow rates increased as cut rate increased. Results in the biased-open mode indicated that the longer port-open duration associated with higher duty cycle at lower cut rates was offset by the increased resistance to the flow of larger, more viscous vitreous particles. In the biased-closed mode, vitreous flow rates increased with increasing cut rate. Results in the biased-closed mode indicated that higher cut rates reduced the viscosity of the vitreous and opened the port more frequently to allow more flow of vitreous. The 23 gauge probes generated the highest vitreous flow rates and 27 gauge probes generated the lowest flow rates at equivalent settings. Maximum vitreous flow was 3.08 ± 0.77 cc/min with 23-gauge probes, 2.31 ± 0.63 cc/min with 25-gauge probes, and 1.34 ± 0.21 cc/min with 27-gauge probes (all probes at 7500 cpm with 650 mmHg vacuum).
Conclusions: :
Higher vitreous flow rates were observed during aspiration at high cut rates. The reduced bite size at higher cut rates reduced the resistance to flow and increased the flow rates. Vitreous aspiration appears to be more efficient at 7500 cpm.
Keywords: vitreous • retinal adhesion