Vitreous flow rates through dual pneumatic cutters: effects of duty cycle and cut rate

Abstract

PurposeWe aimed to investigate effects of instrument settings on porcine vitreous flow rates through dual pneumatic high-speed vitrectomy probes.MethodsThe CONSTELLATION® Vision System was tested with 250, 450, and 650 mmHg of vacuum using six ULTRAVIT® vitrectomy probes of each diameter (25+®, 25, 23, and 20 gauge) operated from 500 cuts per minute (cpm) up to 5,000 cpm. Duty cycle modes tested included biased open, 50/50, and biased closed. Flow rates were calculated by assessing the change in weight of porcine eyes during vitreous aspiration. Volumetric flow rate was measured with a computer-connected electronic scale.ResultsAt lower cut rates, the biased open mode produced higher flow than did the 50/50 mode, which produced higher flow than did the biased closed mode. In the biased closed and 50/50 modes, vitreous flow rates tended to increase with increasing cut rate. Vitreous flow rates in the biased open duty cycle mode remained relatively constant across cut rates.ConclusionVitreous flow rates through dual pneumatic vitrectomy probes could be manipulated by changing the duty cycle modes on the vitrectomy system. Differences in duty cycle behavior suggest that high-speed cut rates of 5,000 cpm may optimize vitreous aspiration.

Fluidics of Single and Double Blade Guillotine Vitrectomy Probes in Balanced Salt Solution and Artificial Vitreous

“…We adopted both BSS and AV in our experiments, as representative of the liquefied vitreous (BSS) and of the vitreous in its gel phase (AV) in order to reproduce as closely as possible, the working conditions during the vitrectomy. Other authors in the past tested vitreous cutters with non-Newtonian viscoelastic fluids, in particular using egg albumen 2 , 13 – 17 or porcine eyes 5 , 15 , 18 ; however, information on the rheologic properties of the fluids were not provided. Using AV, we could test the rheology of the fluid and tune it in such a way that is has properties similar to those of the healthy vitreous.…”

“… 13 – 17 Experiments on vitreous from animal eyes have also been performed. 5 , 15 , 18 The above studies focused on the measurement of the flow rate and its dependency on the working conditions. In recent years Particle Image Velocimetry (PIV) measurements have been introduced to measure the flow field around the tip of vitreous cutters in vitro.…”

Occurrence rate of retinal detachment after small gauge vitrectomy for idiopathic epiretinal membrane

“…A better surgical setting has enhanced flow stability and minimised vitreous turbulences, especially when the vitrectomy probe passes from the vitreous to the balanced salt solution or a dense vitreous base. 17 All together miniaturising and improving vitrectomy systems reduce retinal traction and thereby the risk of iatrogenic retinal breaks. 18,19 In this study, using a 25-gauge system, we found a rate of 8.3% of intraoperative retinal breaks at the end of vitrectomy that could be even overestimated, as any suspicious appearance was considered as an opening and treated.…”

Vitreoretinal instruments: vitrectomy cutters, endoillumination and wide-angle viewing systems

“…6; Additional file 2: video 2). This allows the DC to be controlled independently of the cut rate [19, 24, 37–39] with customized modes: “port biased open” or core mode (the port remains open for the majority of time), 50/50 mode (the port is open 50% of the time) and “biased closed” or shave mode (the port remains closed for the majority of time). Therefore, besides the cut rate and vacuum/aspiration levels, the surgeon can count on another variable in order to control the flow rate.…”