Eyeworld

EW RESIDENTS 70 May 2016 by Mitra Nejad, MD, Jenny Chen, MD, and Wonchon Lin, MD Background As UCLA residents, we have the priv- ilege of operating at 4 separate hos- pitals, each of them with a different phacoemulsification platform. Un- derstanding the various phaco set- tings and occlusion surge minimiz- ing features of each platform helps us maintain safety and efficiency as we rotate through our multiple hospitals. Currently, the Centurion system (Alcon, Fort Worth, Texas) is being used at 2 of our hospitals. Unlike other phaco systems that use gravity-based fluidics, the Centurion system incorporates Active Fluidics technology, which adjusts the IOP by applying pressure to an irrigation bag housed inside the machine. The bag is connected to a balanced dual-segment peristaltic pump, allowing constant monitoring and controlling of IOP. As residents, our utmost priority in learning cataract surgery is to maintain patient safety and to ensure good outcomes. Minimizing IOP fluctuations has been shown to reduce post-occlusion surge, which in turn provides for a safer operation. 1 Minimizing IOP fluctu- ations may also have the benefit of not only reducing post-occlusion surge, but also increasing efficiency (time to lens removal). In a previous laboratory study, Dr. Olson's group examined efficiency and chatter and its relationship to vacuum and flow rate and found a stronger correlation with flow rate than vacuum. 2 In this study, Jensen and colleagues looked at the impact of set intraocular pressure settings with Active Fluidics (vacuum, flow rate and power) on efficiency and chatter. Study summary The study was done on porcine lenses that were prepared in a sim- ilar fashion to previous published studies. 3 The Centurion system was used with a balanced phaco tip with vacuum at 500 mm Hg, aspiration at 35 mL/min, and torsional power at 60%. IOP was tested at 10 mm Hg intervals from 30–110 mm Hg. A lens cube was brought to the phaco tip using vacuum, and then the pha- co pedal was fully depressed while an observer recorded efficiency only when the lens was in contact with the phaco tip. The number of chat- ter events was also recorded. Twenty lens cubes were tested at each inter- val. After the means and standard deviations were calculated for the trials, outliers (more than 2 standard deviations [SDs] from the mean) were removed, and new means and SDs were calculated. Linear regres- sion was used to compare the times for the different groups tested. The authors found a linear relationship between efficiency and IOP among the 9 trials. In other words, increas- ing the IOP led to increased efficien- cy. Also, increasing the IOP led to increased chatter up to an IOP of 50 mm Hg, above which chatter was almost non-existent. Comments Dr. Olson's group has previously published on the validation of the porcine lens preparation used in this study. 3 They found that after their rigorous preparation technique, there was a statistically insignificant difference compared to human lens nuclei in regard to efficiency and chatter. While the authors of this study report that they prepared the porcine lenses similarly to the previ- ous methods, it would be impossible to maintain consistent lens quality, introducing a confounding factor. However, as the authors suggest, it would also be very difficult to create a clinical setting where testing could be limited to 1 variable only. This study provides a unique laboratory method to objectively test various fluidic variables. The density of the human cataract provides its own variable during surgery, which often leads to surgeons adjusting their settings appropriately. The original study on the porcine model used here described that these porcine lens- es were similar to a dense human cataract; in fact, the human lenses being tested were obtained via ex- tracapsular lens extraction cases—a procedure, in current times, reserved for the densest of cataracts. For these denser lenses, many surgeons may add longitudinal power that could contribute to more chatter, even at higher IOP settings. Also, the technique of nucleus disassembly can be very different among sur- geons, which may make more of a difference than variations in settings or even require different settings for maximum efficiency. Further studies on different cataract gradations, disassembly methods, and varying power settings would be more in- formative and applicable to clinical practice. Another variable not discussed in this in-vitro study is other forms of outflow other than aspiration flow rate, such as wound leaks. In gravity-based systems, the surgeon may increase the bottle height to compensate for the fluid egress and maintain the chamber, but this would in turn cause increased turbulence in the anterior cham- ber. Maintaining a set IOP with the Active Fluidics system prevents fluctuations in the anterior chamber and decreases turbulence, which can enhance followability. How will this study be used in clinical practice? Even if the assump- tion was made that the laboratory settings translated perfectly to the operating room surgical setting, it is UCLA residents review "Intraocular pressure study using Centurion phacoemulsification technology" Intraocular pressure study using Centurion phacoemulsification technology Jason Jensen, BS, Tyler Boulter, BS, Nathan Lambert, BS, Brian Zaugg, MD, Brian Stagg, MD, Jeff Pettey, MD, Randall Olson, MD J Cataract Refract Surg (May) 2016;42. Article in press Purpose: To optimize phacoemulsification efficiency by varying the intraocular pressure (IOP), using the Centurion Vision System. Setting: John A. Moran Eye Center Laboratories, University of Utah, Salt Lake City. Design: In vitro laboratory study. Methods: Porcine lenses were soaked in formalin and divided into 2 mm cubes. 0.9 mm, balanced tips were used. Intraocular pressure levels were tested from 30 to 110 mm Hg at 10 mm Hg intervals. Vacuum was set to 500 mm Hg, aspiration to 35 mL/min, and torsional power at 60%. Efficiency (time to lens removal) and chatter (number of lens fragment repulsions from the tip) were measured. Results: Results of the trials showed a linear relationship between efficiency and IOP. Increasing IOP led to an increase in efficiency (i.e., to a decrease in time necessary to remove the lens fragment; R 2 =.5769, P=.0176). Chatter correlated with IOP in the range of 30–50 mm Hg (R 2 =.4506, P=.0448) and was minimal at higher IOPs. Conclusions: Increasing IOP in the Centurion system improved efficiency. Chatter was also decreased or eliminated with increasing IOP. Additional studies will be required to understand the reasons for these findings. Uday Devgan, MD, chief of ophthalmology, Olive View UCLA Medical Center, and clinical professor of ophthalmology, Jules Stein Eye Institute at UCLA continued on page 72 Active fluidic control of IOP is a recent innovation in phaco machines. This study in the May JCRS attempts to analyze the effect on phacodynamics and is reviewed by the UCLA residents. –David F. Chang, MD, EyeWorld journal club editor

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