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Comparison of vacuum rise time, vacuum limit accuracy, and occlusion break surge of 3 new phacoemulsification systems
LABORATORY SCIENCE
Comparison of vacuum rise time, vacuum limit accuracy, and occlusion break surge of 3 new phacoemulsification systems Young Keun Han, MD, Kevin M. Miller, MD
PURPOSE: To compare vacuum rise time, vacuum limit accuracy, and occlusion break surge of 3 new phacoemulsification machines. SETTING: Jules Stein Eye Institute and Department of Ophthalmology, David Geffen School of Medicine at UCLA, Los Angeles, California, USA. METHODS: The vacuum rise time under normal and enhanced aspiration modes, vacuum limit accuracy, and occlusion break surge of the Infiniti Vision System, Stellaris Vision Enhancement System, and WhiteStar Signature Phacoemulsification System were tested. Vacuum rise time and limit accuracy were measured at limit settings of 400 mm Hg and 600 mm Hg. Surge area was recorded at vacuum limit settings of 200 mm Hg, 300 mm Hg, 400 mm Hg, and 500 mm Hg. RESULTS: The Infiniti had the fastest vacuum rise times under normal and enhanced aspiration modes. At 4 seconds, the vacuum limit accuracy was greatest with the Infiniti at the 400 mm Hg limit and the Signature at the 600 mm Hg limit. The Stellaris did not reach either vacuum target. The Infiniti performed better than the other 2 machines during testing of occlusion break surge at all vacuum limit settings above 200 mm Hg. CONCLUSIONS: Under controlled laboratory test conditions, the Infiniti had the fastest vacuum rise time, greatest vacuum limit accuracy at 400 mm Hg, and least occlusion break surge. These results can be explained by the lower compliance of the Infiniti system. J Cataract Refract Surg 2009; 35:1424–1429 Q 2009 ASCRS and ESCRS
The 3 major manufacturers of phacoemulsification systems in the United States are Alcon Laboratories, Abbott Medical Optics (formerly Advanced Medical Optics), and Bausch & Lomb. Each company recently introduced new models. Alcon Laboratories replaced Submitted: December 24, 2008. Final revision submitted: March 5, 2009. Accepted: March 6, 2009. From the Department of Ophthalmology, David Geffen School of Medicine at UCLA and the Jules Stein Eye Institute, Los Angeles, California, USA. Neither author has a financial or proprietary interest in any material or method mentioned. Funded by a gift from the Carl & Roberta Deutsch Foundation, Santa Monica, California, USA. Corresponding author: Kevin M. Miller, MD, Jules Stein Eye Institute, 100 Stein Plaza, UCLA, Los Angeles, California 90095-7002, USA. E-mail: [email protected].
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Q 2009 ASCRS and ESCRS Published by Elsevier Inc.
the Advantec Legacy with the Infiniti Vision System, Abbott Medical Optics replaced the WhiteStar Sovereign with the WhiteStar Signature Phacoemulsification System, and Bausch & Lomb replaced the Millennium Microsurgical System with the Stellaris Vision Enhancement System. According to the manufacturers, the new units incorporate improved fluidics and phacoemulsification technologies to increase the safety and efficacy of cataract surgery. A desirable characteristic of any phaco machine is that it delivers accurate and repeatable fluidic and ultrasound results as requested through the user interface. A major determinant of fluidic system performance is compliance. Compliance is a measure of a system’s ability to expand or contract as a function of applied force. All other things being equal, greater compliance in phacoemulsification systems leads to slower vacuum rise and worse occlusion break surge. The new phacoemulsification systems work in a peristaltic or flow-based mode. When a cataract 0886-3350/09/$dsee front matter doi:10.1016/j.jcrs.2009.03.041
LABORATORY SCIENCE: VACUUM RISE TIME, VACUUM LIMIT ACCURACY, AND OCCLUSION BREAK SURGE IN 3 PHACO SYSTEMS
fragment occludes the needle tip, aspiration flow builds up vacuum in the cassette and tubing. The peristaltic pump stops turning when the preset vacuum limit is reached. Vacuum rise time refers to the time it takes for a machine to reach the vacuum limit. Ideally, the vacuum requested on the console would be the vacuum achieved. Vacuum is useful for holding and manipulating lens fragments inside the eye. Once a fragment is aspirated and clears the lumen of the needle, the potential energy stored in the cassette and tubing suddenly releases, drawing fluid from the anterior chamber to fill the expanded volume in the tubing. This postocclusion break surge of fluid from the anterior chamber is a hazard of cataract surgery. It could be eliminated if cassettes and tubing had zero compliance and the systems were free of trapped air. We were interested in how the 3 new machines perform with respect to each other, so we compared them under tightly controlled laboratory conditions, measuring vacuum rise time, vacuum limit accuracy, and occlusion break surge. MATERIALS AND METHODS An electronic pressure transducer (Foxboro) and a digital storage oscilloscope (Gould Instrument System) were used to measure static and dynamic pressures. The instruments were allowed to warm up at least 15 minutes before use, and calibration of the pressure transducer was verified before each experiment. The Intrepid Fluidic Management System, WhiteStar Signature System fusion pack, and Stellaris Premium AFS phaco pack were each used on each of their respective machines.
Vacuum Rise Time The vertical scale on the oscilloscope was set to 500 mV per division and the time scale, at 1 second per division. After each phacoemulsification machine was primed and tuned according to the manufacturer’s instructions, the irrigation and aspiration lines were connected directly to the pressure transducer (Figure 1). The middle of the drip chamber was placed 90 cm above the pressure transducer, the pressure transducer 83 cm above the ground, and the aspiration flow rate to 30 mL/min on all 3 machines. Because the accuracy of the flow rate influences the vacuum rise time, the flow on all 3 machines was measured by collecting the aspirated fluid for 1 minute and measuring its weight. In the first (standard) experiment, default settings were selected. These included a ‘‘dynamic rise’’ of 0 for the Infiniti, a ‘‘moderate vacuum response’’ for the Stellaris, and the standard setting for the Signature. In the second (enhanced aspiration flow) experiment, the fastest aspiration pump rate adjustment on each machine was selected. These corresponded to a ‘‘dynamic rise’’ of 4 for the Infiniti, the ‘‘fastest vacuum response’’ for the Stellaris, and the maximum pump rate setting (100, 100) for the Signature. A vacuum limit of 400 mm Hg was chosen as clinically relevant and a vacuum level of 600 mm Hg as demanding. Occlusion was simulated by clamping the irrigation line
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Figure 1. Experimental set up for the vacuum rise time experiments. The arrow indicates the location at which the irrigation line was clamped.
within 1 inch of the Luer connector using needle-nosed pliers. After the phacoemulsification footpedal was fully depressed, the vacuum response on the oscilloscope was recorded and the achieved vacuum at time intervals of 0.0, 0.5, 1.0, 2.0, 3.0, and 4.0 seconds was measured.
Occlusion Break Surge For the next experiment, the vertical scale on the oscilloscope was set to 100 mV per division and the time scale to 200 milliseconds per division. To eliminate the bias and uncertainty that different handpieces and different test chambers might introduce, the same phacoemulsification handpiece and test chamber were used for all surge experiments (Figures 2 and 3). The handpiece was an OZil probe with a 0.9 mm straight non-ABS 30degree microtip needle (Alcon Laboratories). All entrapped air was removed from the system before each experiment.
Figure 2. Test chamber for measuring occlusion break surge with a silicone sleeve attached.
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LABORATORY SCIENCE: VACUUM RISE TIME, VACUUM LIMIT ACCURACY, AND OCCLUSION BREAK SURGE IN 3 PHACO SYSTEMS
Figure 3. Experimental setup for occlusion break surge experiments. The arrow indicates the location at which the aspiration line was clamped.
The middle of the drip chamber was placed 90 cm above the test chamber, and the test chamber was placed 83 cm above the ground. Aspiration flow was set at 30 mL/min for all 3 machines. In different experiments, the vacuum limit was set at 200, 300, 400, and 500 mm Hg. These numbers represent the typical working range for most cataract surgeons. After the footpedal on each machine was fully depressed, the aspiration line was clamped with needle-nosed pliers to simulate tip occlusion. Then, the clamp was suddenly released to allow observation of the pressure changes inside the test chamber once the vacuum limit had been reached. The vacuum response in the oscilloscope was recorded and the area under the curve measured (Figure 4).
Statistical Analysis Statistical analysis was performed using the 2-way analysis of variance test. In addition, a multiplicity correction on the 12 man surge area values for the 3 machines at each of the 4 vacuum levels was performed using the Hommel method. A P value of 0.05 or less was considered statistically significant.
Figure 5. Comparison of vacuum rise times at the 400 mm Hg vacuum limit with aspiration flow set to 30 cc/minutes.
Figure 4. Surge area measurement recorded on the oscilloscope. The shaded section beneath the plot represents the surge area. The base of the shaded area represents a positive chamber pressure of 20 mm Hg.
RESULTS The 30 mL/min flow rate was accurate to within 7% of the control panel setting on all 3 machines. Vacuum Rise Time In the standard experiment with an unenhanced 30 mL/min flow setting, the Infiniti reached the 400 mm Hg vacuum limit 0.6 seconds after and the Signature 0.7 seconds after the onset of simulated
Figure 6. Comparison of vacuum rise times at the 400 mm Hg vacuum limit with maximum flow enhancement. The Infiniti showed the fastest rise time.
J CATARACT REFRACT SURG - VOL 35, AUGUST 2009
LABORATORY SCIENCE: VACUUM RISE TIME, VACUUM LIMIT ACCURACY, AND OCCLUSION BREAK SURGE IN 3 PHACO SYSTEMS
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Figure 7. Comparison of vacuum rise times at the 600 mm Hg vacuum limit with aspiration flow set to 30 cc/min.
Figure 8. Comparison of vacuum rise times at the 600 mm Hg vacuum limit with maximum flow enhancement.
occlusion. The Stellaris reached maximum vacuum at 1.1 seconds but did not achieve the preset 400 mm Hg vacuum limit (Figure 5). In the enhanced aspiration flow experiment, the Infiniti reached the 400 mm Hg vacuum limit in 0.6 seconds and the Signature in 0.8 seconds. The Stellaris reached its maximum of 394 mm Hg at 1 second but again did not achieve 400 mm Hg (Figure 6). When the vacuum limit was raised to 600 mm Hg, the Infiniti achieved the vacuum limit in 2.2 seconds and the Signature in 3.3 seconds. The Stellaris did not attain 600 mm Hg within 4 seconds (Figure 7). Under enhanced aspiration flow conditions, the Infiniti reached 600 mm Hg in 1.1 seconds and the Signature in 2.8 seconds. The Stellaris achieved a maximum vacuum of 578 mm Hg at 3 seconds (Figure 8).
At 200 mm Hg, the Infiniti and the Stellaris had zero surge and the Signature had a surge area of 0.36 G 0.06 mm Hg second. As the vacuum limit was increased, the Infiniti performed better than the other 2 machines by a significant margin. At 300 mm Hg, the Infiniti had a surge area of 0.48 G 0.08 mm Hg second, which was 66% less than the Stellaris (1.41 G 0.05 mm Hg second) and 75% less than the Signature (1.94 G 0.06 mm Hg second). At 400 mm Hg, the Infiniti had a surge area of 1.78 G 0.12 mm Hg second, which was 48% less than the Stellaris (3.45 G 0.05 mm Hg second) and 53% less than the Signature (3.82 G 0.13 mm Hg second). At 500 mm Hg, the Infiniti had a surge area of 4.37 G 0.18 mm Hg second, which was 35% less than the Stellaris (6.73 G 0.19 mm Hg second) and 32% less than the Signature (6.46 G 0.12 mm Hg second). The Stellaris performed 27% and 10% better than the Signature at the vacuum levels of 300 mm Hg and 400 mm Hg, respectively, and 4% better at 500 mm Hg (Figure 9). Statistical analysis indicated that the Infiniti produced significantly less surge in the entire test range than the Signature and less surge in the 300 mm Hg to 500 mm Hg interval than the Stellaris. The Stellaris produced significantly less surge in the 200 mm Hg to 400 mm Hg test interval than the Signature.
Vacuum Limit Accuracy None of the 3 machines reached and held the vacuum limits precisely. At the 4-second time point, the Infiniti overshot 400 mm Hg by achieving 404 mm Hg and the Signature by achieving 448 mm Hg. The Stellaris underachieved the vacuum limit at 388 mm Hg (Figure 5). At a preset vacuum limit of 600 mm Hg, the Signature was the closest, with a measured vacuum at 608 mm Hg at 4 seconds. The Infiniti was above at 624 mm Hg, and the Stellaris was under at 578 mm Hg (Figure 7). Occlusion Break Surge All 3 machines exhibited a similar occlusion break response pattern observed on the oscilloscope. The main difference was in the amplitude of the surge curve based on the tested vacuum setting.
DISCUSSION Under tightly controlled laboratory test conditions, the Infiniti had a faster vacuum rise time, greater vacuum limit accuracy at 400 mm Hg, and less occlusion break surge than the Signature and the Stellaris. At a vacuum limit of 600 mm Hg, the Signature had the greatest vacuum limit accuracy.
J CATARACT REFRACT SURG - VOL 35, AUGUST 2009
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LABORATORY SCIENCE: VACUUM RISE TIME, VACUUM LIMIT ACCURACY, AND OCCLUSION BREAK SURGE IN 3 PHACO SYSTEMS
Figure 9. Surge area as a function of aspiration line vacuum at the time of occlusion break.
The accuracy of hitting and achieving the preset vacuum limit is cassette-dependent. We tested 1 cassette from each manufacturer. Had we tested more cassettes or had we adjusted for system vacuum accuracy, it is likely we would have found variations from 1 experiment to the next. The coupling of a cassette’s pressure-sensitive window to the machine’s pressure transducer influences the measured pressure. A common problem with many published studies comparing phaco machines is that they were performed using pig or human cadaver eyes1–4 or in the operating room,5–9 where repeatability is difficult. It is seldom possible to get repeatable results in the same eye 2 trials in a row because of factors such as changing eye-wall compliance, incision leakage, and iris trauma. It is even more difficult to achieve repeatability with different eyes. Our study was performed in a highly controlled laboratory environment that should be reproducible by anyone with the same phaco machines and test equipment. We set up our experiments to control for all known variables, and we were surprised at some our findings. For example, there was no uniformity across manufacturers in bottle height measurements. Bottle height determines infusion pressure, which in part determines the surge response after an occlusion break. The Signature registered a lower bottle height than the other 2 machines; therefore, at the same displayed bottle height, it has an unfair advantage with respect to infusion pressure. We kept the real bottle heights the same in all experiments rather than using the displayed bottle heights. Real bottle height was measured from the handpiece to the middle of the drip chamber. Each phacoemulsification handpiece has a different geometry. To run surge experiments using the
individual handpieces would have required that we use different test chambers, which would have introduced a significant source of bias. Because all the manufacturers’ handpieces are internally rigid, they should have very low compliance. To avoid this bias, we used a common handpiece, needle, and silicone test chamber for all machines in the surge experiments. The only fluidic difference between machines was the compliance of each manufacturer’s tubing and cassette. Several studies1–5 have addressed occlusion break surge; these studies focused on the magnitude of pressure shifts but did not consider the influence of time. We were interested in pressure versus time as this relationship determines fluid flow from the eye after occlusion break. In our surge experiments, we measured the area under the curve. We found that the Infiniti had less occlusion break surge at every vacuum setting; it was approximately 70% less at 300 mm Hg, 50% less at 400 mm Hg, and 30% less at 500 mm Hg. Although factors such as material compliance, tubing length, trapped air, flow rate accuracy, and vacuum limit accuracy could have influenced the outcomes of our experiments, we believe the main difference between the machines we evaluated is the compliance of the cassettes and aspiration tubing. The more compliant a system is, the larger the potential for occlusion break surge and the slower the response time. As mentioned, hitting the pressure limit accurately is dependent on the cassette. As determined indirectly by our testing, the Infiniti Fluidic Management System has a lower compliance than the cassettes of the other machines, which allows it to be more responsive and produce lower occlusion break surge. REFERENCES 1. Ward MS, Georgescu D, Olson RJ. Effect of bottle height and aspiration rate on postocclusion surge in Infiniti and Millennium peristaltic phacoemulsification machines. J Cataract Refract Surg 2008; 34:1400–1402 2. Georgescu D, Payne M, Olson RJ. Objective measurement of postocclusion surge during phacoemulsification in human eye-bank eyes. Am J Ophthalmol 2007; 143:437–440 3. Georgescu D, Kuo AF, Kinard KI, Olson RJ. A fluidics comparison of Alcon Infiniti, Bausch & Lomb Stellaris, and Advanced Medical Optics Signature phacoemulsification machines. Am J Ophthalmol 2008; 145:1014–1017e1 4. Wade M, Isom R, Georgescu D, Olson RJ. Efficacy of cruise control in controlling postocclusion surge with Legacy and Millennium Venturi phacoemulsification machines. J Cataract Refract Surg 2007; 33:1071–1075 5. Wilbrandt HR. Comparative analysis of the fluidics of the AMO Prestige, Alcon Legacy, and Storz Premiere phacoemulsification systems. J Cataract Refract Surg 1997; 23:766–780 6. Davison JA. Performance comparison of the Alcon Legacy 20000 straight and flared 0.9 mm Aspiration Bypass System tips. J Cataract Refract Surg 2002; 28:76–80
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LABORATORY SCIENCE: VACUUM RISE TIME, VACUUM LIMIT ACCURACY, AND OCCLUSION BREAK SURGE IN 3 PHACO SYSTEMS
7. Davison JA. Performance comparison of the Alcon Legacy 20000 1.1 mm TurboSonics and 0.9 mm Aspiration Bypass System tips. J Cataract Refract Surg 1999; 25:1386–1391 8. Davison JA. Performance comparison of the Alcon Legacy 20000 1.1 TurboSonics and 0.9 mm MicroTip. J Cataract Refract Surg 1999; 25:1382–1385 9. Hagan JC III, Davision JA. Clinical comparison of the Alcon 20,000 Legacy and 10,000 Master phacoemulsification units. J Cataract Refract Surg 1998; 24:693–696
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First author: Young Keun Han, MD Department of Ophthalmology, David Geffen School of Medicine at UCLA and the Jules Stein Eye Institute, Los Angeles, California, USA
Comparison of vacuum rise time, vacuum limit accuracy, and occlusion break surge of 3 new phacoemulsification systems Young Keun Han, MD, Kevin M. Miller, MD
PURPOSE: To compare vacuum rise time, vacuum limit accuracy, and occlusion break surge of 3 new phacoemulsification machines. SETTING: Jules Stein Eye Institute and Department of Ophthalmology, David Geffen School of Medicine at UCLA, Los Angeles, California, USA. METHODS: The vacuum rise time under normal and enhanced aspiration modes, vacuum limit accuracy, and occlusion break surge of the Infiniti Vision System, Stellaris Vision Enhancement System, and WhiteStar Signature Phacoemulsification System were tested. Vacuum rise time and limit accuracy were measured at limit settings of 400 mm Hg and 600 mm Hg. Surge area was recorded at vacuum limit settings of 200 mm Hg, 300 mm Hg, 400 mm Hg, and 500 mm Hg. RESULTS: The Infiniti had the fastest vacuum rise times under normal and enhanced aspiration modes. At 4 seconds, the vacuum limit accuracy was greatest with the Infiniti at the 400 mm Hg limit and the Signature at the 600 mm Hg limit. The Stellaris did not reach either vacuum target. The Infiniti performed better than the other 2 machines during testing of occlusion break surge at all vacuum limit settings above 200 mm Hg. CONCLUSIONS: Under controlled laboratory test conditions, the Infiniti had the fastest vacuum rise time, greatest vacuum limit accuracy at 400 mm Hg, and least occlusion break surge. These results can be explained by the lower compliance of the Infiniti system. J Cataract Refract Surg 2009; 35:1424–1429 Q 2009 ASCRS and ESCRS
The 3 major manufacturers of phacoemulsification systems in the United States are Alcon Laboratories, Abbott Medical Optics (formerly Advanced Medical Optics), and Bausch & Lomb. Each company recently introduced new models. Alcon Laboratories replaced Submitted: December 24, 2008. Final revision submitted: March 5, 2009. Accepted: March 6, 2009. From the Department of Ophthalmology, David Geffen School of Medicine at UCLA and the Jules Stein Eye Institute, Los Angeles, California, USA. Neither author has a financial or proprietary interest in any material or method mentioned. Funded by a gift from the Carl & Roberta Deutsch Foundation, Santa Monica, California, USA. Corresponding author: Kevin M. Miller, MD, Jules Stein Eye Institute, 100 Stein Plaza, UCLA, Los Angeles, California 90095-7002, USA. E-mail: [email protected].
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Q 2009 ASCRS and ESCRS Published by Elsevier Inc.
the Advantec Legacy with the Infiniti Vision System, Abbott Medical Optics replaced the WhiteStar Sovereign with the WhiteStar Signature Phacoemulsification System, and Bausch & Lomb replaced the Millennium Microsurgical System with the Stellaris Vision Enhancement System. According to the manufacturers, the new units incorporate improved fluidics and phacoemulsification technologies to increase the safety and efficacy of cataract surgery. A desirable characteristic of any phaco machine is that it delivers accurate and repeatable fluidic and ultrasound results as requested through the user interface. A major determinant of fluidic system performance is compliance. Compliance is a measure of a system’s ability to expand or contract as a function of applied force. All other things being equal, greater compliance in phacoemulsification systems leads to slower vacuum rise and worse occlusion break surge. The new phacoemulsification systems work in a peristaltic or flow-based mode. When a cataract 0886-3350/09/$dsee front matter doi:10.1016/j.jcrs.2009.03.041
LABORATORY SCIENCE: VACUUM RISE TIME, VACUUM LIMIT ACCURACY, AND OCCLUSION BREAK SURGE IN 3 PHACO SYSTEMS
fragment occludes the needle tip, aspiration flow builds up vacuum in the cassette and tubing. The peristaltic pump stops turning when the preset vacuum limit is reached. Vacuum rise time refers to the time it takes for a machine to reach the vacuum limit. Ideally, the vacuum requested on the console would be the vacuum achieved. Vacuum is useful for holding and manipulating lens fragments inside the eye. Once a fragment is aspirated and clears the lumen of the needle, the potential energy stored in the cassette and tubing suddenly releases, drawing fluid from the anterior chamber to fill the expanded volume in the tubing. This postocclusion break surge of fluid from the anterior chamber is a hazard of cataract surgery. It could be eliminated if cassettes and tubing had zero compliance and the systems were free of trapped air. We were interested in how the 3 new machines perform with respect to each other, so we compared them under tightly controlled laboratory conditions, measuring vacuum rise time, vacuum limit accuracy, and occlusion break surge. MATERIALS AND METHODS An electronic pressure transducer (Foxboro) and a digital storage oscilloscope (Gould Instrument System) were used to measure static and dynamic pressures. The instruments were allowed to warm up at least 15 minutes before use, and calibration of the pressure transducer was verified before each experiment. The Intrepid Fluidic Management System, WhiteStar Signature System fusion pack, and Stellaris Premium AFS phaco pack were each used on each of their respective machines.
Vacuum Rise Time The vertical scale on the oscilloscope was set to 500 mV per division and the time scale, at 1 second per division. After each phacoemulsification machine was primed and tuned according to the manufacturer’s instructions, the irrigation and aspiration lines were connected directly to the pressure transducer (Figure 1). The middle of the drip chamber was placed 90 cm above the pressure transducer, the pressure transducer 83 cm above the ground, and the aspiration flow rate to 30 mL/min on all 3 machines. Because the accuracy of the flow rate influences the vacuum rise time, the flow on all 3 machines was measured by collecting the aspirated fluid for 1 minute and measuring its weight. In the first (standard) experiment, default settings were selected. These included a ‘‘dynamic rise’’ of 0 for the Infiniti, a ‘‘moderate vacuum response’’ for the Stellaris, and the standard setting for the Signature. In the second (enhanced aspiration flow) experiment, the fastest aspiration pump rate adjustment on each machine was selected. These corresponded to a ‘‘dynamic rise’’ of 4 for the Infiniti, the ‘‘fastest vacuum response’’ for the Stellaris, and the maximum pump rate setting (100, 100) for the Signature. A vacuum limit of 400 mm Hg was chosen as clinically relevant and a vacuum level of 600 mm Hg as demanding. Occlusion was simulated by clamping the irrigation line
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Figure 1. Experimental set up for the vacuum rise time experiments. The arrow indicates the location at which the irrigation line was clamped.
within 1 inch of the Luer connector using needle-nosed pliers. After the phacoemulsification footpedal was fully depressed, the vacuum response on the oscilloscope was recorded and the achieved vacuum at time intervals of 0.0, 0.5, 1.0, 2.0, 3.0, and 4.0 seconds was measured.
Occlusion Break Surge For the next experiment, the vertical scale on the oscilloscope was set to 100 mV per division and the time scale to 200 milliseconds per division. To eliminate the bias and uncertainty that different handpieces and different test chambers might introduce, the same phacoemulsification handpiece and test chamber were used for all surge experiments (Figures 2 and 3). The handpiece was an OZil probe with a 0.9 mm straight non-ABS 30degree microtip needle (Alcon Laboratories). All entrapped air was removed from the system before each experiment.
Figure 2. Test chamber for measuring occlusion break surge with a silicone sleeve attached.
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LABORATORY SCIENCE: VACUUM RISE TIME, VACUUM LIMIT ACCURACY, AND OCCLUSION BREAK SURGE IN 3 PHACO SYSTEMS
Figure 3. Experimental setup for occlusion break surge experiments. The arrow indicates the location at which the aspiration line was clamped.
The middle of the drip chamber was placed 90 cm above the test chamber, and the test chamber was placed 83 cm above the ground. Aspiration flow was set at 30 mL/min for all 3 machines. In different experiments, the vacuum limit was set at 200, 300, 400, and 500 mm Hg. These numbers represent the typical working range for most cataract surgeons. After the footpedal on each machine was fully depressed, the aspiration line was clamped with needle-nosed pliers to simulate tip occlusion. Then, the clamp was suddenly released to allow observation of the pressure changes inside the test chamber once the vacuum limit had been reached. The vacuum response in the oscilloscope was recorded and the area under the curve measured (Figure 4).
Statistical Analysis Statistical analysis was performed using the 2-way analysis of variance test. In addition, a multiplicity correction on the 12 man surge area values for the 3 machines at each of the 4 vacuum levels was performed using the Hommel method. A P value of 0.05 or less was considered statistically significant.
Figure 5. Comparison of vacuum rise times at the 400 mm Hg vacuum limit with aspiration flow set to 30 cc/minutes.
Figure 4. Surge area measurement recorded on the oscilloscope. The shaded section beneath the plot represents the surge area. The base of the shaded area represents a positive chamber pressure of 20 mm Hg.
RESULTS The 30 mL/min flow rate was accurate to within 7% of the control panel setting on all 3 machines. Vacuum Rise Time In the standard experiment with an unenhanced 30 mL/min flow setting, the Infiniti reached the 400 mm Hg vacuum limit 0.6 seconds after and the Signature 0.7 seconds after the onset of simulated
Figure 6. Comparison of vacuum rise times at the 400 mm Hg vacuum limit with maximum flow enhancement. The Infiniti showed the fastest rise time.
J CATARACT REFRACT SURG - VOL 35, AUGUST 2009
LABORATORY SCIENCE: VACUUM RISE TIME, VACUUM LIMIT ACCURACY, AND OCCLUSION BREAK SURGE IN 3 PHACO SYSTEMS
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Figure 7. Comparison of vacuum rise times at the 600 mm Hg vacuum limit with aspiration flow set to 30 cc/min.
Figure 8. Comparison of vacuum rise times at the 600 mm Hg vacuum limit with maximum flow enhancement.
occlusion. The Stellaris reached maximum vacuum at 1.1 seconds but did not achieve the preset 400 mm Hg vacuum limit (Figure 5). In the enhanced aspiration flow experiment, the Infiniti reached the 400 mm Hg vacuum limit in 0.6 seconds and the Signature in 0.8 seconds. The Stellaris reached its maximum of 394 mm Hg at 1 second but again did not achieve 400 mm Hg (Figure 6). When the vacuum limit was raised to 600 mm Hg, the Infiniti achieved the vacuum limit in 2.2 seconds and the Signature in 3.3 seconds. The Stellaris did not attain 600 mm Hg within 4 seconds (Figure 7). Under enhanced aspiration flow conditions, the Infiniti reached 600 mm Hg in 1.1 seconds and the Signature in 2.8 seconds. The Stellaris achieved a maximum vacuum of 578 mm Hg at 3 seconds (Figure 8).
At 200 mm Hg, the Infiniti and the Stellaris had zero surge and the Signature had a surge area of 0.36 G 0.06 mm Hg second. As the vacuum limit was increased, the Infiniti performed better than the other 2 machines by a significant margin. At 300 mm Hg, the Infiniti had a surge area of 0.48 G 0.08 mm Hg second, which was 66% less than the Stellaris (1.41 G 0.05 mm Hg second) and 75% less than the Signature (1.94 G 0.06 mm Hg second). At 400 mm Hg, the Infiniti had a surge area of 1.78 G 0.12 mm Hg second, which was 48% less than the Stellaris (3.45 G 0.05 mm Hg second) and 53% less than the Signature (3.82 G 0.13 mm Hg second). At 500 mm Hg, the Infiniti had a surge area of 4.37 G 0.18 mm Hg second, which was 35% less than the Stellaris (6.73 G 0.19 mm Hg second) and 32% less than the Signature (6.46 G 0.12 mm Hg second). The Stellaris performed 27% and 10% better than the Signature at the vacuum levels of 300 mm Hg and 400 mm Hg, respectively, and 4% better at 500 mm Hg (Figure 9). Statistical analysis indicated that the Infiniti produced significantly less surge in the entire test range than the Signature and less surge in the 300 mm Hg to 500 mm Hg interval than the Stellaris. The Stellaris produced significantly less surge in the 200 mm Hg to 400 mm Hg test interval than the Signature.
Vacuum Limit Accuracy None of the 3 machines reached and held the vacuum limits precisely. At the 4-second time point, the Infiniti overshot 400 mm Hg by achieving 404 mm Hg and the Signature by achieving 448 mm Hg. The Stellaris underachieved the vacuum limit at 388 mm Hg (Figure 5). At a preset vacuum limit of 600 mm Hg, the Signature was the closest, with a measured vacuum at 608 mm Hg at 4 seconds. The Infiniti was above at 624 mm Hg, and the Stellaris was under at 578 mm Hg (Figure 7). Occlusion Break Surge All 3 machines exhibited a similar occlusion break response pattern observed on the oscilloscope. The main difference was in the amplitude of the surge curve based on the tested vacuum setting.
DISCUSSION Under tightly controlled laboratory test conditions, the Infiniti had a faster vacuum rise time, greater vacuum limit accuracy at 400 mm Hg, and less occlusion break surge than the Signature and the Stellaris. At a vacuum limit of 600 mm Hg, the Signature had the greatest vacuum limit accuracy.
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LABORATORY SCIENCE: VACUUM RISE TIME, VACUUM LIMIT ACCURACY, AND OCCLUSION BREAK SURGE IN 3 PHACO SYSTEMS
Figure 9. Surge area as a function of aspiration line vacuum at the time of occlusion break.
The accuracy of hitting and achieving the preset vacuum limit is cassette-dependent. We tested 1 cassette from each manufacturer. Had we tested more cassettes or had we adjusted for system vacuum accuracy, it is likely we would have found variations from 1 experiment to the next. The coupling of a cassette’s pressure-sensitive window to the machine’s pressure transducer influences the measured pressure. A common problem with many published studies comparing phaco machines is that they were performed using pig or human cadaver eyes1–4 or in the operating room,5–9 where repeatability is difficult. It is seldom possible to get repeatable results in the same eye 2 trials in a row because of factors such as changing eye-wall compliance, incision leakage, and iris trauma. It is even more difficult to achieve repeatability with different eyes. Our study was performed in a highly controlled laboratory environment that should be reproducible by anyone with the same phaco machines and test equipment. We set up our experiments to control for all known variables, and we were surprised at some our findings. For example, there was no uniformity across manufacturers in bottle height measurements. Bottle height determines infusion pressure, which in part determines the surge response after an occlusion break. The Signature registered a lower bottle height than the other 2 machines; therefore, at the same displayed bottle height, it has an unfair advantage with respect to infusion pressure. We kept the real bottle heights the same in all experiments rather than using the displayed bottle heights. Real bottle height was measured from the handpiece to the middle of the drip chamber. Each phacoemulsification handpiece has a different geometry. To run surge experiments using the
individual handpieces would have required that we use different test chambers, which would have introduced a significant source of bias. Because all the manufacturers’ handpieces are internally rigid, they should have very low compliance. To avoid this bias, we used a common handpiece, needle, and silicone test chamber for all machines in the surge experiments. The only fluidic difference between machines was the compliance of each manufacturer’s tubing and cassette. Several studies1–5 have addressed occlusion break surge; these studies focused on the magnitude of pressure shifts but did not consider the influence of time. We were interested in pressure versus time as this relationship determines fluid flow from the eye after occlusion break. In our surge experiments, we measured the area under the curve. We found that the Infiniti had less occlusion break surge at every vacuum setting; it was approximately 70% less at 300 mm Hg, 50% less at 400 mm Hg, and 30% less at 500 mm Hg. Although factors such as material compliance, tubing length, trapped air, flow rate accuracy, and vacuum limit accuracy could have influenced the outcomes of our experiments, we believe the main difference between the machines we evaluated is the compliance of the cassettes and aspiration tubing. The more compliant a system is, the larger the potential for occlusion break surge and the slower the response time. As mentioned, hitting the pressure limit accurately is dependent on the cassette. As determined indirectly by our testing, the Infiniti Fluidic Management System has a lower compliance than the cassettes of the other machines, which allows it to be more responsive and produce lower occlusion break surge. REFERENCES 1. Ward MS, Georgescu D, Olson RJ. Effect of bottle height and aspiration rate on postocclusion surge in Infiniti and Millennium peristaltic phacoemulsification machines. J Cataract Refract Surg 2008; 34:1400–1402 2. Georgescu D, Payne M, Olson RJ. Objective measurement of postocclusion surge during phacoemulsification in human eye-bank eyes. Am J Ophthalmol 2007; 143:437–440 3. Georgescu D, Kuo AF, Kinard KI, Olson RJ. A fluidics comparison of Alcon Infiniti, Bausch & Lomb Stellaris, and Advanced Medical Optics Signature phacoemulsification machines. Am J Ophthalmol 2008; 145:1014–1017e1 4. Wade M, Isom R, Georgescu D, Olson RJ. Efficacy of cruise control in controlling postocclusion surge with Legacy and Millennium Venturi phacoemulsification machines. J Cataract Refract Surg 2007; 33:1071–1075 5. Wilbrandt HR. Comparative analysis of the fluidics of the AMO Prestige, Alcon Legacy, and Storz Premiere phacoemulsification systems. J Cataract Refract Surg 1997; 23:766–780 6. Davison JA. Performance comparison of the Alcon Legacy 20000 straight and flared 0.9 mm Aspiration Bypass System tips. J Cataract Refract Surg 2002; 28:76–80
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7. Davison JA. Performance comparison of the Alcon Legacy 20000 1.1 mm TurboSonics and 0.9 mm Aspiration Bypass System tips. J Cataract Refract Surg 1999; 25:1386–1391 8. Davison JA. Performance comparison of the Alcon Legacy 20000 1.1 TurboSonics and 0.9 mm MicroTip. J Cataract Refract Surg 1999; 25:1382–1385 9. Hagan JC III, Davision JA. Clinical comparison of the Alcon 20,000 Legacy and 10,000 Master phacoemulsification units. J Cataract Refract Surg 1998; 24:693–696
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First author: Young Keun Han, MD Department of Ophthalmology, David Geffen School of Medicine at UCLA and the Jules Stein Eye Institute, Los Angeles, California, USA