Author: David Steel (United Kingdom)
Co-authors: Sonalee Tambat, A. Mani Irannejad, Sina J. Mamouri Mamouri
Purpose
To leverage micro-PIV experiments and validated computational fluid dynamics simulation models to define and compare sphere of influence (SOI) extent and pulsatile motion around vitrectomy probes.
Setting/Venue
Laboratory study using Micro-PIV (Particle Image Velocimetry), CFD (Computational Fluid Dynamics)
Methods
The micro-PIV experiments and simulation models of three probes, namely, 25+® Advanced UltraVit 10,000 cuts per minute (cpm), 25+® HyperVit 20,000 cpm flat and beveled tips were used to compare flow velocity around the probe tip. Vitrectomy system parameters such as applied vacuum settings of 650 mmHg, 50/50 duty cycle setting on the CONSTELLATION® Vision System were applied for both micro-PIV and CFD simulations in a BSS filled beaker. Further CFD simulations were conducted with matched flow rates to compare performance. For micro-PIV, a thin sheet of laser (PurePoint at 525mW) was used to illuminate Polyamid particles dispersed in the beaker. The movement of particles was captured using a high-speed CCD camera. For CFD simulations, a dynamic mesh was used to simulate the motion of the cutter. Flow was assumed to be incompressible and laminar. All products are made by Alcon, Fort Worth, TX.
Results
The micro-PIV results indicate higher fluctuation magnitude for the Advanced UltraVit Bevel probe as compared to the Hypervit probes. There was a slight fluctuation in the velocity profile between consecutive cycles, which may be resulting due to the minor pressure fluctuations inside the probe. Both HyperVit cutters, beveled and flat tips demonstrated a similar behavior. The Reynolds number (representing flow velocity) and Intensity of Root Mean Square (RMS) of the velocity were used in CFD simulations to define extent of SOI and intensity of pulsatile motion, respectively. They were measured on spheres of increasing radii from probe tip and maximum values were recorded. In a quantitative agreement with micro-PIV results, the intensity of velocity fluctuations in CFD simulations was significantly reduced for both HyperVit Probes compared to Advanced UltraVit probe. The Beveled tip of the probe contributed to lowering the flow velocity close to the probe tip (at a distance of r=1 mm) for HyperVit Probes. Such observations hold true for matched-vacuum condition and matched-flow condition. In addition, under matched-flow, the maximum SOI size of HyperVit Probes was smaller compared to that of AdvUltraVit Probe.
Conlusions
Micro-PIV experiments and CFD simulations were used to compare flow dynamics in nearfield of the Vitrectomy probe tip. The flow performance of 25 gauge HYPERVIT probes had more stable aspiration, which was shown by the reduction in the intensity of pulsation of velocity during fluid aspiration. The HyperVit probes showed a smaller SOI compared to advanced UltraVit probes under matched-flow conditions. A smaller SOI and a reduced pulsatile motion may enhance safety of the vitreoretinal surgery. Simulations may help surgeons better understand differences in probe performance and optimize instrument selection.
Financial Disclosure
Research funding: Alcon, Bayer, DORC Consultancy: Gyroscope, Roche
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