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D. C. Buboltz; New Method for Evaluating Flow Rates and Intraocular Pressures During Simulated Vitreoretinal Surgeries. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3612.
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Hypertony and hypotony are potentially hazardous during vitreoretinal surgery, but flow rates and resultant intraocular pressures (IOPs) are not always evident from instrumental settings. Moreover, "open-sky" experimental setups do not appropriately represent in vivo conditions. Proper experimental conditions are necessary for accurate flow rate and IOP measurements during vitreoretinal surgery. Flow rate measurements with an open-system set up may yield inaccurate results as infusion pressure is not accounted for and IOP cannot be measured. A closed-system eye model more closely simulates flow rates through a human eye.In this study, a system was developed to measure flow rates and IOP during simulated vitrectomy using a closed system that accounted for the effects of infusion.
Model eyes were constructed from acrylic domes. Holes were drilled in the tops of the globes, in a configuration replicating pars plana incision sites. Trocar cannulae were glued into 23-, 25+- or 25-gauge holes, but were not required for 20-gauge holes. A vitrectomy probe was inserted into one hole, and an infusion line was inserted into the other hole. A fluid flow meter was attached to the infusion cannula. A hole was drilled into the bottom of each globe, where a pressure transducer was attached to record IOP. Balanced salt solution was infused at 30 mmHg. Flow and pressure data were relayed to a computer via a data acquisition board. Three vitrectomy systems were tested with various instrumental settings, including different levels of applied vacuum.
The system was capable of reproducibly measuring flow rates, with a coefficient of variation generally <=10% among multiple probes. The system also was capable of reproducibly measuring IOP values, and could detect conditions that could yield extreme hypotony. For example, slow-flow conditions could yield IOP within 10% of the set pressure, but with fasterhigher-flow conditions, high pressure loss from the infusion cannula could yield hypotonous IOP values. The system was capable of quantifying the effects of the IOP compensation feature of one vitrectomy system, which maintained IOP values at levels close to the expected pressure setting.
The model eye system was useful for investigating flow rates and intraocular pressures that could occur during a vitreoretinal surgery, and was useful for identifying surgical conditions that could yield potentially unsafe intraocular pressures.
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