William R. Barlow

Optimum on-time duty cycle for micropulse technology

Purpose To evaluate the optimum on time for the most efficient removal of lens fragments using micropulsed ultrasound (US). Setting John A. Moran Eye Center Laboratories, University of Utah, Salt Lake City, Utah, USA. Design Experimental study. Methods Twenty porcine lens nuclei were soaked in formalin for 2 hours and then divided into 2.0 mm cubes. Using an US machine with a 0.9 mm bent and a 30‐degree bevel tip, the on time was varied every millisecond (ms) from 2 ms to 10 ms with the off time kept constant at 10 ms. Efficiency (time to lens removal) and chatter (number of lens fragment repulsions from the tip) were determined. Results The most efficient phacoemulsification was achieved with an on time of 6 ms. On times shorter than 6 ms were significantly less efficient (R2 = .82, P=.04). Greater on times did not result in a significant difference in efficiency (R2 = .03, P=.78) but did appear to have more chatter events when comparing 9 to 10 ms with 2 to 8 ms (P<.0001). Conclusions With micropulsed longitudinal US, a 6 ms on time was equally as efficient as longer on times, while shorter on times (2 to 5 ms) had decreased efficiency. At 9 ms and 10 ms on time, significantly more chatter was noted. Therefore, to maximize phacoemulsification, an on‐time setting of 6 ms is recommended. Financial Disclosure No author has a financial or proprietary interest in any material or method mentioned.

Phacoemulsification efficiency with a radiused phaco tip

Purpose To evaluate radiused and nonradiused phacoemulsification tips to determine which tip is more efficient in removal of lens fragments using 3 ultrasound (US) modalities. Setting John A. Moran Eye Center Laboratories, University of Utah, Salt Lake City, Utah, USA. Design Experimental study. Methods Porcine lens nuclei were formalin‐soaked for 2 hours or 3 hours and then divided into 2.0 mm cubes. Thirty‐degree, 0.9 mm beveled radiused tips and nonradiused tips were used with torsional, transverse, and micropulsed US modalities. Bent tips were used with torsional and transversal US, and straight tips were used with micropulsed US. Efficiency (time to lens removal) and chatter (number of lens fragment repulsions from the tip) were determined. Results The mean phacoemulsification efficiency was statistically significantly decreased (increased time for removal) with the radiused tip compared with the nonradiused tip for torsional US only (2‐hour soaked lenses: 2.14 seconds ± 1.94 [SD] versus 1.18 ± 0.69 seconds [P < .05]; 3‐hour soaked lenses: 5.07 ± 4.2 seconds versus 2.52 ± 1.99 seconds [P < .05]). There was no difference in chatter results. Conclusion The radiused tip showed decreased efficiency with torsional US only. Financial Disclosure No author has a financial or proprietary interest in any material or method mentioned.

Effect of phaco tip diameter on efficiency and chatter.

Purpose To evaluate 3 phacoemulsification tips of different sizes and determine which size is most efficient in lens fragment removal using 3 ultrasound (US) approaches. Setting John A. Moran Eye Center Laboratories, University of Utah, Salt Lake City, Utah, USA. Design Experimental study. Methods Porcine lens nuclei were formalin‐soaked for 2 hours then divided into 2.0 mm cubes; 1.1 mm, 0.9 mm, and 0.7 mm phaco tips were used with torsional and micropulsed US. The 1.1 mm tips were unavailable for torsional US, so 0.9 mm and 0.7 mm tips were used. Efficiency (amount of time for lens removal) and chatter (number of lens‐fragment repulsions from the tip) were determined. Results The mean phacoemulsification efficiency was highest with the 0.9 mm tip for all US variations. There were statistically significant differences between the 0.9 mm and 0.7 mm tips with micropulsed US (0.8 seconds ± 0.29 [SD] versus 1.4 ± 0.93 seconds; P=.0112) and transversal US (0.8 ± 0.17 seconds versus 1.4 ± 0.89 seconds; P=.0065). There was no significant difference between 0.9 mm and 0.7 mm tips with torsional US or between the 1.1 mm and 0.9 mm tips with micropulsed or transversal US; however, trends were identical, with 0.9 mm tips performing better than 0.7 mm and 1.1 mm tips. Conclusion With all 3 systems, the 0.9 mm tip was most efficient, with the fewest outliers and smallest standard deviation. Financial Disclosure No author has a financial or proprietary interest in any material or method mentioned.

Determining Optimal Torsional Ultrasound Power for Cataract Surgery With Automatic Longitudinal Pulses at Maximum Vacuum Ex Vivo

PURPOSE To determine the optimal longitudinal power settings for Infiniti OZil Intelligent Phaco (IP) at varying torsional amplitude settings; and to test the hypothesis that increasing longitudinal power is more important at lower torsional amplitudes to achieve efficient phacoemulsification. DESIGN Laboratory investigation. METHODS setting: John A. Moran Eye Center, University of Utah, Salt Lake City, Utah. procedure: Individual porcine nuclei were fixed in formalin, then cut into 2.0 mm cubes. Lens cube phacoemulsification was done using OZil IP at 60%, 80%, and 100% torsional amplitude with 0%, 10%, 20%, 30%, 50%, 75%, or 100% longitudinal power. All experiments were done using a 20 gauge 0.9 mm bent reverse bevel phaco tip at constant vacuum (550 mm Hg), aspiration rate (40 mL/min), and bottle height (50 cm). main outcome measure: Complete lens particle phacoemulsification (efficiency). RESULTS Linear regression analysis showed a significant increase in efficiency with increasing longitudinal power at 60% torsional amplitude (R(2) = 0.7269, P = .01) and 80% torsional amplitude (R(2) = 0.6995, P = .02) but not at 100% amplitude (R(2) = 0.3053, P = .2). Baseline comparison of 60% or 80% vs 100% torsional amplitude without longitudinal power showed increased efficiency at 100% (P = .0004). Increasing longitudinal power to 20% abolished the efficiency difference between 80% vs 100% amplitudes. In contrast, 75% longitudinal power abolished the efficiency difference between 60% vs 100% torsional amplitudes. CONCLUSIONS Results suggest that longitudinal power becomes more critical at increasing phacoemulsification efficiencies at torsional amplitudes less than 100%. Increasing longitudinal power does not further increase efficiency at maximal torsional amplitudes.

Impact of micropulsed ultrasound power settings on the efficiency and chatter associated with lens-fragment removal

Purpose To determine the optimum power settings in micropulsed ultrasound (US). Setting John A. Moran Eye Center Laboratories, University of Utah, Salt Lake City, Utah, USA. Design Experimental study. Methods Pig lenses hardened to be comparable to dense human cataracts were cut into 2.0 mm cubes and removed using micropulsed longitudinal US with previously optimized settings (6 milliseconds on and 6 milliseconds off and using a 0.9 mm 30‐degree beveled bent phaco tip). The aspiration was set at 40 mL/min and the vacuum level at 550 mm Hg. Twenty lens cubes were tested with the power set from 10% to 100% in increments of 10%. Primary outcome measures were efficiency time (time to lens removal) and chatter (number of times the lens fragment visibly bounced off the tip). Results Efficiency time decreased with increasing power. There was a correlation between power and efficiency time (R2 = 0.41, P = .046), which was more substantial between 30% and 100% power (R2 = 0.71, P = .004). The mean number of chatter events did not differ significantly between power settings (R2 = 0.012, P = .1195). Conclusions There was a 5‐fold increase in efficiency between 10% power and 20% power, which likely indicates that there is a minimum power threshold for efficient breakup of the lens. Between 20% and 100% power, there was a linear, strong, and statistically significant improvement in efficiency in these lens fragments. In addition, with micropulsed US there was little chatter or microchatter throughout the power range. Financial Disclosure No author has a financial or proprietary interest in any material or method mentioned.

Effect of increased vacuum and aspiration rates on phacoemulsification efficiency

Purpose To evaluate the effect of vacuum and aspiration rates on phacoemulsification efficiency. Setting John A. Moran Eye Center Laboratories, University of Utah, Salt Lake City, Utah, USA. Design Experimental study. Methods Formalin‐soaked porcine lenses were divided into 2.0 mm cubes, and 0.9 mm 30‐degree beveled 20‐degree bent tips were used with micropulse ultrasound (US) (6 milliseconds on and 6 milliseconds off) and a peristaltic flow system. Vacuum levels were tested at 200, 300, 400, and 500 mm Hg, and aspiration rates were tested at 20, 35, and 50 mL/min. Efficiency (time to lens removal) and chatter (number of lens fragment repulsions from the tip) were determined. Results Increasing vacuum increased efficiency only when going from 200 mm Hg to higher vacuum levels. Increasing aspiration increased efficiency at all points measured (25 mL/min versus 35 mL/min, P < .0001; 35 mL/min versus 50 mL/min, P = .012; 25 mL/min versus 50 mL/min, P < .0001). Chatter was highest at 200 mm Hg and decreased when vacuum was increased from 200 mm Hg to 300 mm Hg and up. Chatter decreased with increasing flow. Conclusions Vacuum improved efficiency only up to 300 mm Hg and was more dependent on increasing flow. Similarly, chatter correlated with 200 mm Hg vacuum only and was more correlated with flow. Limitations of this study include use of only 1 US power modulation and hard nuclear material. Financial Disclosure No author has a financial or proprietary interest in any material or method mentioned.

Torsional power study using CENTURION phacoemulsification technology.

To evaluate the effect of varying levels of power on phacoemulsification efficiency using the CENTURION Vision System.

Comparison of venturi and peristaltic vacuum in phacoemulsification.

Purpose To evaluate the efficiency of peristaltic‐based and venturi‐based vacuums. Setting John A. Moran Eye Center Laboratories, University of Utah, Salt Lake City, Utah, USA. Design Experimental study. Methods Porcine lenses were hardened with formalin and cut into 2.0 mm cubes. Time to fragment removal (efficiency) and fragment bounces off the tip (chatter) were measured using a Signature machine with the ability to switch between peristaltic‐based and venturi‐based vacuum. Micropulse longitudinal and transversal ultrasound motions were tested. Results Venturi‐based vacuum had increased efficiency and decreased chatter compared with peristaltic‐based vacuum at lower vacuum levels. Conclusion Use of a venturi‐based vacuum, when available, may result in reduced clearance time of lens material and mitigate chatter even under noisy conditions. Financial Disclosure No author has a financial or proprietary interest in any material or method mentioned.

Bent versus straight tips in micropulsed longitudinal phacoemulsification

OBJECTIVE The aim of this study was to evaluate bent and straight phacoemulsification tips to determine which tip is more efficient in removal of lens fragments, using micropulsed longitudinal ultrasound in phacoemulsification. DESIGN In vitro laboratory study. METHODS The John A. Moran Eye Center Laboratories, University of Utah, Salt Lake City, Utah, was the study setting. Pig lenses hardened in a manner comparable with dense human cataracts were cut into 2-mm cubes and removed with micropulsed longitudinal ultrasound using settings previously shown to be optimally efficient (6 milliseconds on and 6 milliseconds off for a bent tip). To verify this time as most efficient for a straight tip, we also tested times of 5, 6, and 7 milliseconds time on and off. The tips were either straight or with a 20-degree bend. Twenty cubes were used for each comparative run. RESULTS For the straight tip, 6 milliseconds on (1.56 ± 0.815 seconds) was significantly more efficient than 7 milliseconds on (2.45 ± 1.56 seconds, p = 0.001) and not significantly more efficient than 5 milliseconds on (1.69 ± 0.86 seconds, p = 0.43). Five milliseconds off time (1.45 ± 0.76s) was more efficient than 6 milliseconds (2.06 ± 1.37 seconds, p = 0.004) and 7 milliseconds off (2.18 ± 1.24s, p = 0.001). The straight tip was more efficient than the bent tip (1.38 ± 0.83 versus 2.93 ± 2.14 seconds, p = 0.006). CONCLUSIONS Results are contrary to accepted common belief. Micropulsed longitudinal phacoemulsification is more efficient with a straight rather than a bent tip.

Thermal evaluation of two phacoemulsification systems.

OBJECTIVE To compare thermal profiles of new transversal ultrasound power modulation to torsional ultrasound in an artificial chamber and cadaver eye. DESIGN Laboratory investigation. METHODS John A. Moran Eye Center Laboratories, University of Utah, Salt Lake City, Utah, was the study setting. Temperature increase after 30 seconds was measured at the needle midshaft in an artificial chamber and at maximal friction point in a cadaver eye. Ellips FX (transverse) was tested at 100% power, as was Signature with micropulse settings (6 milliseconds on and off). OZil (torsional only) was tested at 100% power in the artificial chamber and cadaver eye. Runs were completed with aspiration blocked. Temperature was continuously measured on the phacoemulsification sleeve using a microthermistor probe connected to the BAT-10 multipurpose thermometer, with an accuracy of ±0.1°C. RESULTS Transversal FX had a greater temperature increase than micropulse (p < 0.001) and torsional (p < 0.001). Micropulse had a greater temperature increase than torsional (p < 0.001). The cadaver eye had a greater temperature increase than the artificial chamber for torsional (p < 0.001). CONCLUSIONS Higher heat accumulation and potential for incisional burn occurred with the cadaver model than with the artificial chamber, suggesting the need for caution when using 100% torsional ultrasound with aspiration blocked. Transversal FX generated more heat than was reported originally. Further study is needed to determine the incidence of incisional burn with varied power settings for this new model. Micropulse generated more heat than previous reports, but the increased efficiency is likely to negate potentially increased incisional burn risk.