- Email: [email protected]
Impact of torsional micropulse on phacoemulsification efficiency and chatter
Impact of torsional micropulse on phacoemulsification efficiency and chatter Sami W. Kabbara, MD,* Joshua Heczko, MD,y Brian Ta, BS,y Ashlie Bernhisel, MD,y William Barlow, MD,y Brian Zaugg, MD,y Randall J. Olson, MD,y Jeff Pettey, MDy ABSTRACT RESUM E Objective: Evaluate the effect of increasing ultrasound (US) power on chatter events and efficiency under both continuous and micropulse torsional US to reduce total cataract extraction times. Design: In vitro laboratory study. Methods: Porcine lens nuclei were incubated in formalin for 2 hours and then cut into 2-mm cubes. Phacoemulsification was performed using the Centurion Vision System and Infiniti OZil handpiece with the balanced tip. Both US modalities were studied at 60%, 80%, and 100% power. Micropulse rate was 83 pulses per second with 50% on time. Each combination comprised 20 runs. Efficiency was considered as the total time for a cube to be emulsified; chatter was the number of times the lens fragment bounced off the tip. Results: There was significant decrease in efficiency when power was increased from 60% to 100% (1.331.97 s; p < 0.001) under micropulse US and significant increase in chatter when power was further increased to 100% from 60% (0.150.94 s; p < 0.001). There was no significant efficiency change with increased power under continuous US. Comparing the phacoemulsification efficiency between continuous and micropulse US, we found no significant difference at 60% and 80% power; at 100% power, continuous was significantly more efficient than micropulse (1.48 and 1.97 s, respectively; p = 0.001). Conclusions: Increasing power above 60% decreased efficiency under torsional micropulse US. We believe that this was due to the chatter increase observed with increasing US power. Torsional continuous US was significantly more efficient than micropulse US at 100% power. Objectif: Évaluer l’effet de l’augmentation de la puissance des ultrasons torsionnels en mode continu et en mode micropulsé sur l’efficacité et le degré de répulsion des fragments (chatter) avec l’objectif de raccourcir la durée totale d’extraction de la cataracte. Nature: Étude in vitro en laboratoire. Méthodes: Après fixation au formol pendant 2 heures, des noyaux cristalliniens de porc ont été découpés en cubes de 2,0 mm. Les cubes ont alors été soumis à une phacoémulsification (CenturionÒ Vision System, pièce à main OZilÒ de Infiniti et pointes Balanced) aux réglages suivants: puissance de 60 %, de 80 % et de 100 % en modes continu et micropulsé. Le taux de micropulsion était de 83 pulsions/seconde à 50 % de la durée de marche. Chaque combinaison a fait l’objet de 20 passages en machine. L’efficacité correspondait au temps total nécessaire à l’émulsification d’un cube; le degré de répulsion des fragments correspondait au nombre de fois que le fragment de cristallin a rebondi sur la pointe. Résultats: On a enregistré une baisse significative au chapitre de l’efficacité lorsque la puissance est passée de 60 % à 100 % (1,33–1,97 s; p < 0,001) en mode micropulsé de même qu’une hausse significative du degré de répulsion des fragments lorsque la puissance est passée de 60 % à 100 % (0,15–0,94 s; p < 0,001). On n’a enregistré aucune différence significative au chapitre de l’efficacité en mode continu à mesure qu’augmentait la puissance. Lors de cette comparaison de l’efficacité de la phacoémulsification opposant le mode continu et le mode micropulsé, nous n’avons noté aucune différence significative à une puissance de 60 % et de 80 %; par contre, à la puissance de 100 %, le mode continu a été significativement plus efficace que le mode micropulsé (1,48 s et 1,97 s, respectivement; p = 0,001). Conclusions: L’augmentation de la puissance au-delà de 60 % a réduit l’efficacité des ultrasons torsionnels en mode micropulsé. Nous sommes d’avis que ce phénomène tient à l’augmentation du degré de répulsion des fragments à mesure qu’augmente la puissance. À une puissance de 100 %, les ultrasons torsionnels en mode continu étaient significativement plus efficaces que les ultrasons en mode micropulsé.
Phacoemulsification, first introduced by Dr. Charles Kelman in 1967, has revolutionized the world of cataract extraction.1 Since its inception, phacoemulsification has undergone many advances, making it the standard of care for cataract removal in the developed world.2 Such improvements include better control over various settings such as power and fluidics, which directly influence the duration of the surgery and in turn patient safety.3 Our lab has been involved in a multitude of studies researching optimal phacoemulsification settings in a porcine
© 2019 Canadian Ophthalmological Society. Published by Elsevier Inc. All rights reserved. https://doi.org/10.1016/j.jcjo.2019.02.016 ISSN 0008-4182
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model.412 In one study using the Whitestar machine (Abbott Medical Optics, Inc. / Johnson & Johnson Vision, Santa Ana, CA), micropulse (410 ms on time) was determined to be superior in efficiency over long pulse (3060 ms on time) and continuous ultrasound (US) under low vacuum and aspiration settings but comparable in efficiency under higher settings.8 In our series we have determined the optimal longitudinal micropulse on and off times to be 6 ms.6,7 In addition, micropulse US reduces the total amount of energy delivered to the eye
Role of torsional micropulse in phacoemulsification—Kabbara et al. compared with continuous US, which can decrease heatrelated surgical complications.13,14 In contrast to longitudinal micropulse US, no previous studies have looked at the role of torsional micropulse US on lens extraction. A feature available in the Centurion Vision System (Alcon Surgical, Fort Worth, Tex.), torsional US causes the phaco tip to oscillate laterally, subtending an arc while in constant contact with the lens. Using the optimal on- and off-time settings identified for the Whitestar,6,7 we aimed to examine the role of Centurion’s torsional micropulse feature (83 pulses per second [PPS]) on efficiency and chatter.
TAGEDH1MATERIALS AND METHODSTAGEDEN Because this study did not include human subjects, institutional review board approval was not required. Lens preparation and cubing
Porcine lenses were prepared to resemble hard (3 to 4+) human cataract lenses in density and behaviour during phacoemulsification.5 The pig eyes were purchased from Visiontech Inc (Sunnyvale, Tex.) and then dissected within 48 hours of arrival. The lens nuclei were fixed in 10 mL of 10% neutral buffered formalin for 2 hours and then washed 3 times with balanced salt solution (BSS). The lenses were kept in BSS for 24 hours at room temperature. Afterward, the lenses were cut into 2.0-mm cubes.4 The lens cubes were then placed in BSS solution to allow for calibration. The phacoemulsification experiments were done within 24 hours postcubing.
Phacoemulsification
Phacoemulsification of the lens cubes was performed using the Centurion Vision System. Experiments were carried out using the OZil INFINITI handpiece with the balanced tip. Vacuum was set at 500 mm Hg, aspiration rate at 50 mL/min, and intraocular pressure (IOP) at 50 mm Hg in accordance with the previously determined optimal phacoemulsification settings.15 Continuous and micropulse torsional US were each studied at power settings of 60%, 80%, and 100%. Pulse rate was set at 83 PPS with 50% on time, which is equivalent to the Whitestar micropulse setting of 6 ms on and 6 ms off. The Centurion feature OZil Intelligent Phaco (IP) was turned on. Each combination comprised 20 runs for a total of 120 runs. Efficiency (the total time for a cube to be emulsified excluding the chatter time) and chatter (number of times the lens fragment bounced off the tip) were measured and recorded as previously described.4,5 One randomly chosen cube from the centre of the container was placed inside a small rubber chamber, which was attached to the handpiece and filled with BSS. Phacoemulsification was performed consistently by the same author (S.W.K.) across all trials. Time measurement was started upon initiation of the
phacoemulsification process; a handheld stopwatch was used by the same author (J.H.) across all trials. Every time the particle bounced off, the time was stopped, and an event of chatter was recorded. The vacuum was then reactivated, and the time resumed once the particle reoccluded the tip. Therefore, efficiency was considered to be the total time it took to emulsify the lens cube, excluding the chatter time delay. Statistical analysis
Efficiency times were averaged and a standard deviation (SD) was calculated. Time points more than 2 SDs away from the mean were not considered in the final analysis. The new mean and SD were then recalculated. A linear regression with a calculated R2 was used to compare the efficiency times obtained from various groups and was also used to determine whether there was a significant change in chatter events with parameter changes (Microsoft Excel, Redmond, Wash.).
TAGEDH1RESULTSTAGEDEN Pulsed US
Our results demonstrate that, as the power increases, efficiency decreases under pulsed US of 83 PPS (Fig. 1). There was a significant decrease in efficiency when the power was raised from 60% to 80% (1.331.865 s; p = 0.02). Moreover, there was a significant decrease in efficiency when the power was increased from 60% to 100% (1.331.97 s; p < 0.001); however, there was no significant decrease in efficiency when the power was increased from 80% to 100% (1.861.97 s; p = 0.20). Chatter events also were significantly increased when the power was increased from 60% to 80% (p = 0.02; Fig. 2). Similarly, there was a significant increase in chatter events when the power was further increased to 100% from 60% (p 0.001); however, there was no significant increase in chatter events when the power was increased from 80% to 100% (p = 0.5). Furthermore, there was a significant increase in cumulative dissipated energy (CDE) as the power was increased from 60% to 80% (0.42 to 0.69; p = 0.003; Table 1) and a significant increase as the power was increased from 60% to 100%
Fig. 1—Effect of torsional micropulse ultrasound on efficiency at 60%, 80%, and 100% power. R2 = 0.87. CAN J OPHTHALMOL—VOL. 54, NO. 5, OCTOBER 2019
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Role of torsional micropulse in phacoemulsification—Kabbara et al. Table 3—Effect of continuous torsional US on chatter at 60%, 80%, and 100% power Power (%) 60 80 100
Mean Chatter Event § SD 0 0.42 § 0.76 0.35 § 0.48
Significant p values for chatter events between 60% and 80% power and 60% and 100% power were 0.01 and 0.004, respectively.
Fig. 2—Effect of torsional micropulse ultrasound on chatter at 60%, 80%, and 100% power. R2 = 0.92.
Table 1—Cumulative dissipated energy (CDE) with varying power under continuous and micropulse ultrasound (US) Power
CDE Micropulse US*
60% 80% 100%
0.42 0.69 0.79
There was a significant increase in CDE as the power was increased from 60% to 80% (0.47 to 0.65; p = 0.007; Table 1) and from 60% to 100% (0.47 to 0.63; p < 0.001). Despite an increase in CDE when the power was increased from 80% to 100%, the difference was not statistically significant (p = 0.80). When comparing the phacoemulsification efficiency between continuous and pulsed US, we found no significant difference at 60% and 80% power. However, at 100% power, continuous US was significantly more efficient than micropulse US (1.48 and 1.97 s, respectively; p = 0.001; Table 2).
Continuous USy 60% 80% 100%
0.47 0.65 0.63
* Under micropulse US, there was significant difference between 60% and 80% and 60% and 100% power, p = 0.003 and <0.001, respectively. y Under continuous US, there was significant difference between 60% and 80% and 60% and 100% power, p = 0.007 and <0.001, respectively.All other differences had p > 0.05.
(0.42 to 0.79; p < 0.001). There was also an increase in CDE when the power was increased from 80% to 100%; however, the difference was not statistically significant (p = 0.28).
Continuous US
There was no statistically significant change in efficiency with increased power under continuous power mode (Table 2). Eighty percent power was the least efficient out of the 3 power settings, with a mean efficiency of 1.79 s compared with 1.50 and 1.48 s at 60% and 100% power, respectively. Chatter also appeared to be the highest at 80% power, with a mean of 0.42 chatter events that was significantly higher than the mean chatter at 60% power (p = 0.01; Table 3). Moreover, at 60% power, there were significantly fewer chatter events than at 100% power (0.35 events; p = 0.004). There was no significant difference between chatter events occurring at 80% and 100% power (p = 0.7). Table 2—Comparison of the effect of continuous and micropulse ultrasound (US) on efficiency Power (%)
60 80 100
Continuous US,* Mean Efficiency (seconds) § SD
Micropulse US,y Mean Efficiency (seconds) § SD
p
1.50 § 0.47 1.79 § 0.42 1.48 § 0.35
1.33 § 0.15 1.86 § 0.75 1.97 § 0.94
0.30 0.77 0.001
p >0.05 between all power setting under continuous US. y Under micropulse US, there was significant difference between 60% and 80% and 60% and 100% power, p = 0.02 and <0.001, respectively. *
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TAGEDH1DISCUSSIONTAGEDEN A complication with using phacoemulsification US in cataract surgery is endothelial damage secondary to factors such as long phacoemulsification time and high US energy.9,16 An advantage of using torsional US is the reduced free radical production that occurs secondary to cavitation bubbles generated by the phacoemulsification process; this in turn has a potentially protective effect on the corneal endothelium.17,18 Objective studies looking at the optimal settings that increase efficiency and reduce chatter are important in producing favourable surgical outcomes and increased patient satisfaction. To our knowledge, our study is the first to look at micropulsing under torsional US. Our previous studies, which have looked at optimal on and off times on the Whitestar Signature machine, demonstrated that 6 ms on and off times (equivalent to 83 PPS) had the highest phacoemulsification efficiency with the lowest chatter events.6,7 Using a similar pulse setting of 83 PPS, we examined how an increase in power affected efficiency and chatter on the Centurion machine. We found that efficiency decreased as power was increased above 60%, with the optimal power setting of 60%. This was contrary to our previous micropulse studies on the Whitestar, where we found a linear improvement in efficiency as longitudinal power was increased above 20%.10 The current study’s results also were inconsistent with previous long-pulse studies on the Whitestar machine, which showed increased efficiency with increased US power.8 In this study we tested a different US energy delivery mechanism using torsional US with its lateral movement of the phaco tip, as opposed to the longitudinal action used in previous studies. It is not entirely surprising that a different mechanism of US delivery would behave differently under otherwise similar environments. We also found a significant increase in chatter events as the power was increased from 60% to 100%. This largely accounts for the decreased efficiency at 83 PPS with increased power and was consistent with previous studies
Role of torsional micropulse in phacoemulsification—Kabbara et al. demonstrating a strong correlation between increased chatter and decreased efficiency.4 It is clear that pulsed torsional US, combined with bursts of longitudinal phaco via the IP mechanism, has a repulsive effect at higher power levels. In addition, a power setting of 60% yielded significantly less CDE than both 80% and 100% power. Hence, for a surgeon using these settings for pulse torsional US, we recommend that the power setting be set at 60% because of its increased efficiency and lower overall generated energy. Although not tested in this series, it is also possible that power levels below 60% may result in improved efficiency over higher levels; however, further studies evaluating micropulse are needed to evaluate this hypothesis, similar to our previous work evaluating incremental increases in continuous US.19 When comparing the effect of power on efficiency between continuous and micropulse settings, we found continuous US to be significantly more efficient at 100% power. This finding warrants further comparison between the micropulse and continuous settings. The 83 PPS setting could be an optimal rate only for longitudinal micropulsing, but not for torsional pulse, because tip-complextip-action with such short on-time duration might be acting as a repulsing force. However, it is important to note that we did not observe a significant difference in efficiency between all the examined power settings under continuous US. Nevertheless, more studies are needed to look at different torsional pulse rates in order to further understand this phenomenon and its impact on phacoemulsification efficiency. There were several limitations in our study. First, the phacoemulsification runs were conducted in vitro, which allowed us to control various parameters, such as consistency of lens density, that would not be possible in vivo during cataract surgery. Moreover, the porcine cubes were equivalent to 3 to 4+ nuclear cataract, 2-mm cube lens fragments, which would differ from the shape and size of the actual lens fragments encountered during surgery but allowed for consistent lens fragments for evaluation. Nevertheless, in previous studies we demonstrated that our porcine lens model is comparable to human lenses.5 Our study also is subject to human error because the person who held the handpiece and performed the phacoemulsification verbally signalled to the timekeeper to start keeping time at the beginning and ending of phacoemulsification process and whenever chatter events occurred. To minimize such errors, the same authors performed all time measurements and fragment phacoemulsification across all experimental runs so as to allow errors (if any) to be equally distributed across all trials. In conclusion, we found that increasing power decreased efficiency under torsional micropulsing. We believe that this was due to a significant increase in chatter that we observed with increased power. Moreover, torsional continuous US was significantly more efficient than micropulse US at 100% power. Further studies are needed to look at the impact of various pulsing rates and power settings on efficiency and to better define their utility in cataract surgery.
TAGEDH1REFERENCESTAGEDEN 1. Pandey SK, Milverton EJ, Maloof AJ. A tribute to Charles David Kelman MD: ophthalmologist, inventor and pioneer of phacoemulsification surgery. Clin Exp Ophthalmol. 2004;32:529–33. 2. Shah PA, Yoo S. Innovations in phacoemulsification technology. Curr Opin Ophthalmol. 2007;18:23–6. 3. Fishkind WJ. The phaco machine: analysing new technology. Curr Opin Ophthalmol. 2013;24:41–6. 4. DeMill DL, Zaugg BE, Pettey JH, et al. Objective comparison of 4 nonlongitudinal ultrasound modalities regarding efficiency and chatter. J Cataract Refract Surg. 2012;38:1065–71. 5. Oakey ZB, Jensen JD, Zaugg BE, Radmall BR, Pettey JH, Olson RJ. Porcine lens nuclei as a model for comparison of 3 ultrasound modalities regarding efficiency and chatter. J Cataract Refract Surg. 2013;39:1248–53. 6. Jensen JD, Kirk KR, Gupta I, et al. Determining optimal ultrasound off time with micropulse longitudinal phacoemulsification. J Cataract Refract Surg. 2015;41:433–6. 7. Kirk KR, Ronquillo Jr C, Jensen JD, et al. Optimum on-time duty cycle for micropulse technology. J Cataract Refract Surg. 2014;40: 1545–8. 8. Gardiner GL, Garff K, Gupta I, et al. Effect of pulsing ultrasound on phacoemulsification efficiency. J Cataract Refract Surg. 2015;41:2560–4. 9. Fishkind W, Bakewell B, Donnenfeld ED, Rose AD, Watkins LA, Olson RJ. Comparative clinical trial of ultrasound phacoemulsification with and without the WhiteStar system. J Cataract Refract Surg. 2006;32:45–9. 10. Garff K, Jensen JD, Cahoon J, et al. Impact of micropulsed ultrasound power settings on the efficiency and chatter associated with lens-fragment removal. J Cataract Refract Surg. 2015;41:1264–7. 11. Kabbara SW, Heczko JB, Bernhisel AA, et al. Effect of high vacuum and aspiration on phacoemulsification efficiency and chatter using a transversal ultrasound machine. J Cataract Refract Surg. 2018;44:1378–83. 12. Kabbara S, Heczko J, Ta B, et al. Determining optimal ultrasound percent on time with long pulse torsional phacoemulsification. Can J Ophthalmol. 2019;54:395–8. 13. Payne M, Waite A, Olson RJ. Thermal inertia associated with ultrapulse technology in phacoemulsification. J Cataract Refract Surg. 2006;32: 1032–4. 14. Bradley MJ, Olson RJ. A survey about phacoemulsification incision thermal contraction incidence and causal relationships. Am J Ophthalmol. 2006;141:222–4. 15. Ronquillo Jr CC, Zaugg B, Stagg B, et al. Determining optimal torsional ultrasound power for cataract surgery with automatic longitudinal pulses at maximum vacuum ex vivo. Am J Ophthalmol. 2014;158:1262–6. 16. O’Brien PD, Fitzpatrick P, Kilmartin DJ, Beatty S. Risk factors for endothelial cell loss after phacoemulsification surgery by a junior resident. J Cataract Refract Surg. 2004;30:839–43. 17. Aust SD, Terry S, Hebdon T, Gunderson B, Terry M, Dimalanta R. Determining the local origin of hydroxyl radical generation during phacoemulsification. J Cataract Refract Surg. 2011;37:1154–9. 18. Topaz M, Motiei M, Assia E, Meyerstein D, Meyerstein N, Gedanken A. Acoustic cavitation in phacoemulsification: chemical effects, modes of action and cavitation index. Ultrasound Med Biol. 2002;28:775–84. 19. Jensen JD, Shi DS, Robinson MS, et al. Torsional power study using CENTURION phacoemulsification technology. Clin Exp Ophthalmol. 2016;44:710–3.
Footnotes and Disclosure: This work was supported in part by an unrestricted grant from Research to Prevent Blindness, Inc, New York, NY, to the Department of Ophthalmology and Visual Sciences, University of Utah, Salt Lake City, UT, and by Dr. Zaugg’s Achievement Reward from the College Scientists Foundation Scholar program (ARCS Foundation Utah, Salt Lake City, UT.) CAN J OPHTHALMOL—VOL. 54, NO. 5, OCTOBER 2019
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Role of torsional micropulse in phacoemulsification—Kabbara et al. Dr. Olson is on the scientific advisory board of EyeGate Pharmaceuticals and of Perfect Lens. Conflicts of interest for all other authors: none. From the *BannerUniversity of Arizona College of Medicine, Phoenix, AZ; yDepartment of Ophthalmology and Visual Sciences, John A. Moran Eye Center, University of Utah, Salt Lake City, UT
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Originally received Aug. 29, 2018. Final revision Jan. 31, 2019. Accepted Feb. 5, 2019. Correspondence to: Jeff Pettey, MD, John A. Moran Eye Center, University of Utah, 65 Mario Capecchi Drive, Salt Lake City, UT 84132, USA. [email protected]
Phacoemulsification, first introduced by Dr. Charles Kelman in 1967, has revolutionized the world of cataract extraction.1 Since its inception, phacoemulsification has undergone many advances, making it the standard of care for cataract removal in the developed world.2 Such improvements include better control over various settings such as power and fluidics, which directly influence the duration of the surgery and in turn patient safety.3 Our lab has been involved in a multitude of studies researching optimal phacoemulsification settings in a porcine
© 2019 Canadian Ophthalmological Society. Published by Elsevier Inc. All rights reserved. https://doi.org/10.1016/j.jcjo.2019.02.016 ISSN 0008-4182
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model.412 In one study using the Whitestar machine (Abbott Medical Optics, Inc. / Johnson & Johnson Vision, Santa Ana, CA), micropulse (410 ms on time) was determined to be superior in efficiency over long pulse (3060 ms on time) and continuous ultrasound (US) under low vacuum and aspiration settings but comparable in efficiency under higher settings.8 In our series we have determined the optimal longitudinal micropulse on and off times to be 6 ms.6,7 In addition, micropulse US reduces the total amount of energy delivered to the eye
Role of torsional micropulse in phacoemulsification—Kabbara et al. compared with continuous US, which can decrease heatrelated surgical complications.13,14 In contrast to longitudinal micropulse US, no previous studies have looked at the role of torsional micropulse US on lens extraction. A feature available in the Centurion Vision System (Alcon Surgical, Fort Worth, Tex.), torsional US causes the phaco tip to oscillate laterally, subtending an arc while in constant contact with the lens. Using the optimal on- and off-time settings identified for the Whitestar,6,7 we aimed to examine the role of Centurion’s torsional micropulse feature (83 pulses per second [PPS]) on efficiency and chatter.
TAGEDH1MATERIALS AND METHODSTAGEDEN Because this study did not include human subjects, institutional review board approval was not required. Lens preparation and cubing
Porcine lenses were prepared to resemble hard (3 to 4+) human cataract lenses in density and behaviour during phacoemulsification.5 The pig eyes were purchased from Visiontech Inc (Sunnyvale, Tex.) and then dissected within 48 hours of arrival. The lens nuclei were fixed in 10 mL of 10% neutral buffered formalin for 2 hours and then washed 3 times with balanced salt solution (BSS). The lenses were kept in BSS for 24 hours at room temperature. Afterward, the lenses were cut into 2.0-mm cubes.4 The lens cubes were then placed in BSS solution to allow for calibration. The phacoemulsification experiments were done within 24 hours postcubing.
Phacoemulsification
Phacoemulsification of the lens cubes was performed using the Centurion Vision System. Experiments were carried out using the OZil INFINITI handpiece with the balanced tip. Vacuum was set at 500 mm Hg, aspiration rate at 50 mL/min, and intraocular pressure (IOP) at 50 mm Hg in accordance with the previously determined optimal phacoemulsification settings.15 Continuous and micropulse torsional US were each studied at power settings of 60%, 80%, and 100%. Pulse rate was set at 83 PPS with 50% on time, which is equivalent to the Whitestar micropulse setting of 6 ms on and 6 ms off. The Centurion feature OZil Intelligent Phaco (IP) was turned on. Each combination comprised 20 runs for a total of 120 runs. Efficiency (the total time for a cube to be emulsified excluding the chatter time) and chatter (number of times the lens fragment bounced off the tip) were measured and recorded as previously described.4,5 One randomly chosen cube from the centre of the container was placed inside a small rubber chamber, which was attached to the handpiece and filled with BSS. Phacoemulsification was performed consistently by the same author (S.W.K.) across all trials. Time measurement was started upon initiation of the
phacoemulsification process; a handheld stopwatch was used by the same author (J.H.) across all trials. Every time the particle bounced off, the time was stopped, and an event of chatter was recorded. The vacuum was then reactivated, and the time resumed once the particle reoccluded the tip. Therefore, efficiency was considered to be the total time it took to emulsify the lens cube, excluding the chatter time delay. Statistical analysis
Efficiency times were averaged and a standard deviation (SD) was calculated. Time points more than 2 SDs away from the mean were not considered in the final analysis. The new mean and SD were then recalculated. A linear regression with a calculated R2 was used to compare the efficiency times obtained from various groups and was also used to determine whether there was a significant change in chatter events with parameter changes (Microsoft Excel, Redmond, Wash.).
TAGEDH1RESULTSTAGEDEN Pulsed US
Our results demonstrate that, as the power increases, efficiency decreases under pulsed US of 83 PPS (Fig. 1). There was a significant decrease in efficiency when the power was raised from 60% to 80% (1.331.865 s; p = 0.02). Moreover, there was a significant decrease in efficiency when the power was increased from 60% to 100% (1.331.97 s; p < 0.001); however, there was no significant decrease in efficiency when the power was increased from 80% to 100% (1.861.97 s; p = 0.20). Chatter events also were significantly increased when the power was increased from 60% to 80% (p = 0.02; Fig. 2). Similarly, there was a significant increase in chatter events when the power was further increased to 100% from 60% (p 0.001); however, there was no significant increase in chatter events when the power was increased from 80% to 100% (p = 0.5). Furthermore, there was a significant increase in cumulative dissipated energy (CDE) as the power was increased from 60% to 80% (0.42 to 0.69; p = 0.003; Table 1) and a significant increase as the power was increased from 60% to 100%
Fig. 1—Effect of torsional micropulse ultrasound on efficiency at 60%, 80%, and 100% power. R2 = 0.87. CAN J OPHTHALMOL—VOL. 54, NO. 5, OCTOBER 2019
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Role of torsional micropulse in phacoemulsification—Kabbara et al. Table 3—Effect of continuous torsional US on chatter at 60%, 80%, and 100% power Power (%) 60 80 100
Mean Chatter Event § SD 0 0.42 § 0.76 0.35 § 0.48
Significant p values for chatter events between 60% and 80% power and 60% and 100% power were 0.01 and 0.004, respectively.
Fig. 2—Effect of torsional micropulse ultrasound on chatter at 60%, 80%, and 100% power. R2 = 0.92.
Table 1—Cumulative dissipated energy (CDE) with varying power under continuous and micropulse ultrasound (US) Power
CDE Micropulse US*
60% 80% 100%
0.42 0.69 0.79
There was a significant increase in CDE as the power was increased from 60% to 80% (0.47 to 0.65; p = 0.007; Table 1) and from 60% to 100% (0.47 to 0.63; p < 0.001). Despite an increase in CDE when the power was increased from 80% to 100%, the difference was not statistically significant (p = 0.80). When comparing the phacoemulsification efficiency between continuous and pulsed US, we found no significant difference at 60% and 80% power. However, at 100% power, continuous US was significantly more efficient than micropulse US (1.48 and 1.97 s, respectively; p = 0.001; Table 2).
Continuous USy 60% 80% 100%
0.47 0.65 0.63
* Under micropulse US, there was significant difference between 60% and 80% and 60% and 100% power, p = 0.003 and <0.001, respectively. y Under continuous US, there was significant difference between 60% and 80% and 60% and 100% power, p = 0.007 and <0.001, respectively.All other differences had p > 0.05.
(0.42 to 0.79; p < 0.001). There was also an increase in CDE when the power was increased from 80% to 100%; however, the difference was not statistically significant (p = 0.28).
Continuous US
There was no statistically significant change in efficiency with increased power under continuous power mode (Table 2). Eighty percent power was the least efficient out of the 3 power settings, with a mean efficiency of 1.79 s compared with 1.50 and 1.48 s at 60% and 100% power, respectively. Chatter also appeared to be the highest at 80% power, with a mean of 0.42 chatter events that was significantly higher than the mean chatter at 60% power (p = 0.01; Table 3). Moreover, at 60% power, there were significantly fewer chatter events than at 100% power (0.35 events; p = 0.004). There was no significant difference between chatter events occurring at 80% and 100% power (p = 0.7). Table 2—Comparison of the effect of continuous and micropulse ultrasound (US) on efficiency Power (%)
60 80 100
Continuous US,* Mean Efficiency (seconds) § SD
Micropulse US,y Mean Efficiency (seconds) § SD
p
1.50 § 0.47 1.79 § 0.42 1.48 § 0.35
1.33 § 0.15 1.86 § 0.75 1.97 § 0.94
0.30 0.77 0.001
p >0.05 between all power setting under continuous US. y Under micropulse US, there was significant difference between 60% and 80% and 60% and 100% power, p = 0.02 and <0.001, respectively. *
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TAGEDH1DISCUSSIONTAGEDEN A complication with using phacoemulsification US in cataract surgery is endothelial damage secondary to factors such as long phacoemulsification time and high US energy.9,16 An advantage of using torsional US is the reduced free radical production that occurs secondary to cavitation bubbles generated by the phacoemulsification process; this in turn has a potentially protective effect on the corneal endothelium.17,18 Objective studies looking at the optimal settings that increase efficiency and reduce chatter are important in producing favourable surgical outcomes and increased patient satisfaction. To our knowledge, our study is the first to look at micropulsing under torsional US. Our previous studies, which have looked at optimal on and off times on the Whitestar Signature machine, demonstrated that 6 ms on and off times (equivalent to 83 PPS) had the highest phacoemulsification efficiency with the lowest chatter events.6,7 Using a similar pulse setting of 83 PPS, we examined how an increase in power affected efficiency and chatter on the Centurion machine. We found that efficiency decreased as power was increased above 60%, with the optimal power setting of 60%. This was contrary to our previous micropulse studies on the Whitestar, where we found a linear improvement in efficiency as longitudinal power was increased above 20%.10 The current study’s results also were inconsistent with previous long-pulse studies on the Whitestar machine, which showed increased efficiency with increased US power.8 In this study we tested a different US energy delivery mechanism using torsional US with its lateral movement of the phaco tip, as opposed to the longitudinal action used in previous studies. It is not entirely surprising that a different mechanism of US delivery would behave differently under otherwise similar environments. We also found a significant increase in chatter events as the power was increased from 60% to 100%. This largely accounts for the decreased efficiency at 83 PPS with increased power and was consistent with previous studies
Role of torsional micropulse in phacoemulsification—Kabbara et al. demonstrating a strong correlation between increased chatter and decreased efficiency.4 It is clear that pulsed torsional US, combined with bursts of longitudinal phaco via the IP mechanism, has a repulsive effect at higher power levels. In addition, a power setting of 60% yielded significantly less CDE than both 80% and 100% power. Hence, for a surgeon using these settings for pulse torsional US, we recommend that the power setting be set at 60% because of its increased efficiency and lower overall generated energy. Although not tested in this series, it is also possible that power levels below 60% may result in improved efficiency over higher levels; however, further studies evaluating micropulse are needed to evaluate this hypothesis, similar to our previous work evaluating incremental increases in continuous US.19 When comparing the effect of power on efficiency between continuous and micropulse settings, we found continuous US to be significantly more efficient at 100% power. This finding warrants further comparison between the micropulse and continuous settings. The 83 PPS setting could be an optimal rate only for longitudinal micropulsing, but not for torsional pulse, because tip-complextip-action with such short on-time duration might be acting as a repulsing force. However, it is important to note that we did not observe a significant difference in efficiency between all the examined power settings under continuous US. Nevertheless, more studies are needed to look at different torsional pulse rates in order to further understand this phenomenon and its impact on phacoemulsification efficiency. There were several limitations in our study. First, the phacoemulsification runs were conducted in vitro, which allowed us to control various parameters, such as consistency of lens density, that would not be possible in vivo during cataract surgery. Moreover, the porcine cubes were equivalent to 3 to 4+ nuclear cataract, 2-mm cube lens fragments, which would differ from the shape and size of the actual lens fragments encountered during surgery but allowed for consistent lens fragments for evaluation. Nevertheless, in previous studies we demonstrated that our porcine lens model is comparable to human lenses.5 Our study also is subject to human error because the person who held the handpiece and performed the phacoemulsification verbally signalled to the timekeeper to start keeping time at the beginning and ending of phacoemulsification process and whenever chatter events occurred. To minimize such errors, the same authors performed all time measurements and fragment phacoemulsification across all experimental runs so as to allow errors (if any) to be equally distributed across all trials. In conclusion, we found that increasing power decreased efficiency under torsional micropulsing. We believe that this was due to a significant increase in chatter that we observed with increased power. Moreover, torsional continuous US was significantly more efficient than micropulse US at 100% power. Further studies are needed to look at the impact of various pulsing rates and power settings on efficiency and to better define their utility in cataract surgery.
TAGEDH1REFERENCESTAGEDEN 1. Pandey SK, Milverton EJ, Maloof AJ. A tribute to Charles David Kelman MD: ophthalmologist, inventor and pioneer of phacoemulsification surgery. Clin Exp Ophthalmol. 2004;32:529–33. 2. Shah PA, Yoo S. Innovations in phacoemulsification technology. Curr Opin Ophthalmol. 2007;18:23–6. 3. Fishkind WJ. The phaco machine: analysing new technology. Curr Opin Ophthalmol. 2013;24:41–6. 4. DeMill DL, Zaugg BE, Pettey JH, et al. Objective comparison of 4 nonlongitudinal ultrasound modalities regarding efficiency and chatter. J Cataract Refract Surg. 2012;38:1065–71. 5. Oakey ZB, Jensen JD, Zaugg BE, Radmall BR, Pettey JH, Olson RJ. Porcine lens nuclei as a model for comparison of 3 ultrasound modalities regarding efficiency and chatter. J Cataract Refract Surg. 2013;39:1248–53. 6. Jensen JD, Kirk KR, Gupta I, et al. Determining optimal ultrasound off time with micropulse longitudinal phacoemulsification. J Cataract Refract Surg. 2015;41:433–6. 7. Kirk KR, Ronquillo Jr C, Jensen JD, et al. Optimum on-time duty cycle for micropulse technology. J Cataract Refract Surg. 2014;40: 1545–8. 8. Gardiner GL, Garff K, Gupta I, et al. Effect of pulsing ultrasound on phacoemulsification efficiency. J Cataract Refract Surg. 2015;41:2560–4. 9. Fishkind W, Bakewell B, Donnenfeld ED, Rose AD, Watkins LA, Olson RJ. Comparative clinical trial of ultrasound phacoemulsification with and without the WhiteStar system. J Cataract Refract Surg. 2006;32:45–9. 10. Garff K, Jensen JD, Cahoon J, et al. Impact of micropulsed ultrasound power settings on the efficiency and chatter associated with lens-fragment removal. J Cataract Refract Surg. 2015;41:1264–7. 11. Kabbara SW, Heczko JB, Bernhisel AA, et al. Effect of high vacuum and aspiration on phacoemulsification efficiency and chatter using a transversal ultrasound machine. J Cataract Refract Surg. 2018;44:1378–83. 12. Kabbara S, Heczko J, Ta B, et al. Determining optimal ultrasound percent on time with long pulse torsional phacoemulsification. Can J Ophthalmol. 2019;54:395–8. 13. Payne M, Waite A, Olson RJ. Thermal inertia associated with ultrapulse technology in phacoemulsification. J Cataract Refract Surg. 2006;32: 1032–4. 14. Bradley MJ, Olson RJ. A survey about phacoemulsification incision thermal contraction incidence and causal relationships. Am J Ophthalmol. 2006;141:222–4. 15. Ronquillo Jr CC, Zaugg B, Stagg B, et al. Determining optimal torsional ultrasound power for cataract surgery with automatic longitudinal pulses at maximum vacuum ex vivo. Am J Ophthalmol. 2014;158:1262–6. 16. O’Brien PD, Fitzpatrick P, Kilmartin DJ, Beatty S. Risk factors for endothelial cell loss after phacoemulsification surgery by a junior resident. J Cataract Refract Surg. 2004;30:839–43. 17. Aust SD, Terry S, Hebdon T, Gunderson B, Terry M, Dimalanta R. Determining the local origin of hydroxyl radical generation during phacoemulsification. J Cataract Refract Surg. 2011;37:1154–9. 18. Topaz M, Motiei M, Assia E, Meyerstein D, Meyerstein N, Gedanken A. Acoustic cavitation in phacoemulsification: chemical effects, modes of action and cavitation index. Ultrasound Med Biol. 2002;28:775–84. 19. Jensen JD, Shi DS, Robinson MS, et al. Torsional power study using CENTURION phacoemulsification technology. Clin Exp Ophthalmol. 2016;44:710–3.
Footnotes and Disclosure: This work was supported in part by an unrestricted grant from Research to Prevent Blindness, Inc, New York, NY, to the Department of Ophthalmology and Visual Sciences, University of Utah, Salt Lake City, UT, and by Dr. Zaugg’s Achievement Reward from the College Scientists Foundation Scholar program (ARCS Foundation Utah, Salt Lake City, UT.) CAN J OPHTHALMOL—VOL. 54, NO. 5, OCTOBER 2019
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Role of torsional micropulse in phacoemulsification—Kabbara et al. Dr. Olson is on the scientific advisory board of EyeGate Pharmaceuticals and of Perfect Lens. Conflicts of interest for all other authors: none. From the *BannerUniversity of Arizona College of Medicine, Phoenix, AZ; yDepartment of Ophthalmology and Visual Sciences, John A. Moran Eye Center, University of Utah, Salt Lake City, UT
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Originally received Aug. 29, 2018. Final revision Jan. 31, 2019. Accepted Feb. 5, 2019. Correspondence to: Jeff Pettey, MD, John A. Moran Eye Center, University of Utah, 65 Mario Capecchi Drive, Salt Lake City, UT 84132, USA. [email protected]