DESIGN: Experimental study.METHODS: An acrylic test chamber was used to model the anterior chamber of the eye. Two passive (gravity-based) systems were tested using bottle heights yielding infusion pressures of 41, 75, and 109 cm of water under zero-flow conditions. One actively controlled system was tested using equivalent target IOPs of 30, 55, and 80 mm Hg. Test chamber IOPs were measured at aspiration flow rates of 15, 30, 45, and 60 cc/min. RESULTS:The measured flow rates were similar between fluidics systems across the range of intended aspiration flow rates. All systems achieved the desired target IOPs under zero-flow conditions. After activation of aspiration flow, however, measured IOPs decreased from target IOPs for the 2 passive systems. Each 15 cc/min increase in the aspiration flow rate produced a pressure drop of 14.0 to 16.2 mm Hg or 9.3 to 14.2 mm Hg, depending on the system. Measured IOPs in the actively controlled system closely matched the targeted IOPs across all tested aspiration flow rates, deviating from targets by no more than 4.3 mm Hg.CONCLUSIONS: All phacoemulsification aspiration infusion fluidics systems achieved target IOPs under zero-flow conditions. Only the actively controlled system maintained target IOPs across a range of aspiration flow rates. These experimental findings suggest that anterior chamber stability might be better in the clinical setting using an actively controlled system. Financial Disclosure: Dr. Dimalanta is an employee of Alcon Research, Ltd. Dr. Miller is an investigator and speaker for and a consultant to Alcon Laboratories, Inc. Dr. Nicoli has no financial or proprietary interest in any material or method mentioned. J Cataract Refract Surg 2016; 42:157-162 Q 2016 ASCRS and ESCRSAnterior chamber maintenance is one of the keys to successful outcomes in phacoemulsification cataract surgery.1 One primary factor in maintaining a safe and stable anterior chamber is controlling intraocular pressure (IOP) to stay within or near the physiologic range.2 However, large fluctuations in IOP can occur during cataract surgery.3 An IOP that is too high can cause ocular discomfort, decreased ocular perfusion, accelerated glaucomatous optic nerve damage, and postoperative corneal edema. 4,5 An IOP that is too low or that fluctuates widely can lead to instability or collapse of the anterior chamber, ocular discomfort, and trauma to anterior segment structures such as the cornea, iris, and lens capsule. In passive or gravity-based phacoemulsification aspiration devices, pressure and flow are inversely related; increased flow results in decreased pressure and vice versa, in particular when the source pressure is held constant.7 During phacoemulsification, inflow supplied by the irrigation line equals outflow under steady-state conditions. Total outflow is the sum of flow through the aspiration line and leakage through the incisions.8 If incision leakage is zero, the infusion flow rate equals the aspiration flow rate. Because

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