Determining optimal ultrasound off time with micropulse longitudinal phacoemulsification

Optimization of Phacoemulsification Tip Gauge on the Oertli CataRhex3 in an in vitro Setting

Purpose

To evaluate the effect of each of the tip sizes available for the Oertli CataRhex3^® phacoemulsification machine on efficiency.

Methods

Porcine lenses were fixed in formalin for 2 hours, then cut into 3.0 mm cubes. We studied three Oertli tips, all of which had a 30-degree bevel: easyTip 2.2 mm (20G), easyTip 2.8 mm (19G), and CO-MICS (21G). For the 19G and 20G tips, vacuum was set at 600 mmHg, irrigation rate at 50 mL/min, continuous power 70%, and bottle height 85 cm. For the 21G tip, vacuum was set at 450 mmHg; irrigation and power settings were identical to those used for the easyTip tips. We measured time to removal and chatter events to determine efficiency.

Results

Results from 20 trials for each tip showed that the larger the gauge size, the more quickly lens fragments were removed. Chatter events demonstrated an increasing trend with smaller tip gauge. The 19G tip used an average time to fragment removal of 2.8 seconds; the 20G, 3.2 seconds; and the 21G, 4.6 seconds. Increasing tip diameter from 21G to 20G decreased emulsification time by 33% (P = 0.02). Increasing the diameter from 21G to 19G further decreased time to emulsification by 42% (P = 0.003). The 21G tip had a mean 1.4 events/cube; 20G, 0.35 events; and 19G, 0.1 events. Differences in mean chatter events for each tip were each statistically significant.

Conclusion

These data suggest that when evaluated by chatter events and emulsification time, the 2.8 mm (19G) easyTip proves to have greatest efficiency.

Optimizing Tip Diameter in Phacoemulsification of Varying Lens Sizes: An in vitro Study

Purpose

We assessed the effect of two lens cube sizes, three tip sizes, and two ultrasound (US) approaches on phacoemulsification efficiency and chatter.

Methods

After porcine lens nuclei were soaked in formalin, we divided them into cubes measuring 2.0 mm or 3.0 mm. We collected efficiency and chatter data for 30-degree bent 19 G, 20 G, and 21 G tips with a continuous torsional US system; and for straight 19 G, 20 G, and 21 G tips with a micropulse longitudinal US system.

Results

The average time needed for removal was always higher for the 3.0 mm lens cube than for the 2.0 mm lens cube. Statistically significant differences were observed between the 19 G and 21 G tips with micropulse longitudinal US using a 2.0 mm cube and a 3.0 mm cube, and with continuous transversal US using a 2.0 mm lens cube and a 3.0 mm cube. We did not observe significant differences between 19 G and 20 G tips with either cube size in either US system. However, we noted identical trends for both cube sizes with both US approaches; 19 G tips performed better than 20 G and 21 G tips.

Conclusion

Regardless of the lens size, 19 G needles were the most efficient, and had both the fewest outliers and the smallest standard deviations.

Optimum on-time and off-time combinations for micropulse phacoemulsification in venturi vacuum mode

PURPOSE

To measure the time to fragment removal and number of chatter events using various combinations of micropulse on times and off times (measured in milliseconds) of longitudinal ultrasound (US) using a venturi-based phacoemulsification system.

SETTING

John A. Moran Eye Center, University of Utah, Salt Lake City, USA.

DESIGN

Experimental study.

METHODS

Pig lenses were hardened with formalin and cut into 2.0 mm cubes. The time to fragment removal (efficiency) and frequency of fragments bouncing off the tip (chatter) were measured with the venturi-based system. Micropulse longitudinal US was tested. Parameters were combinations of 5, 6, and 7 milliseconds on, with 5, 6, and 7 milliseconds off. Twenty runs each of 9 combinations were completed.

RESULTS

There was a statistically significant difference between on/off duty cycle combinations. The 6 on/7 off group had higher efficiency than the 5 on/6 off and 7 on/7 off groups. Six on/5 off was more efficient than 5 on/6 off. When data were pooled and on times alone were used, 6 milliseconds on time was more efficient than 5 or 7 milliseconds. No efficiency differences in off times were found. No significant chatter differences were observed.

CONCLUSIONS

Using micropulse longitudinal US in venturi vacuum mode, 6 milliseconds on was the most efficient on time. Five, 6, and 7 milliseconds off times had similar efficiency. These data suggest that the most efficient setting with lowest US energy use is 6 milliseconds on and 7 milliseconds off.

Impact of torsional micropulse on phacoemulsification efficiency and chatter

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% (1.33-1.97 s; p < 0.001) under micropulse US and significant increase in chatter when power was further increased to 100% from 60% (0.15-0.94 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.

Phacoemulsification in review: Optimization of cataract removal in an in vitro setting

Phacoemulsification, initially used in the late 1960s, continues to be the standard of care for cataract removal. An animal model was developed so that, in a controlled research setting, all the various machines, handpieces, tips, and settings could be investigated. As a general rule, the higher power, vacuum, and aspiration settings lead to optimally efficient phacoemulsification. In addition, both new phacoemulsification platforms and newly developed devices have been shown to improve efficiency. As a result, we recommend that the integration of these recent developments should be considered in future investigations.

Determining optimal ultrasound percent on time with long-pulse torsional phacoemulsification

OBJECTIVE

To evaluate the optimum percent on time for the most efficient lens fragment removal using long-pulse torsional ultrasound (US).

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. Vacuum was set at 500 mm Hg, aspiration rate at 50 mL/min, and intraocular pressure (IOP) at 50 mm Hg. Pulse rate was 26 pulses/second. Studied parameters were percent power: 60%, 80%, and 100%, and percent on times: 50%, 60%, 70%, and 80%. Efficiency was 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 no significant difference in efficiency between 50%, 60%, and 70 % on-time settings (p = 0.17 and 0.08, respectively); however, there was significant increase in efficiency when the on time was increased from 70% to 80% (p = 0.03). Increasing power from 60% to 100% showed a statistically significant efficiency increase (p = 0.001). There was no significant change in chatter with increasing on time; however, there was a statistically significant increase in chatter with every power level increase.

CONCLUSION

Increasing on-time percent does not improve efficiency under torsional long-pulse US. There is no significant change in chatter with increasing on-time percent. Increasing power increases efficiency despite chatter increase. Long-pulse US does not appear to influence torsional action in a clinically meaningful way.

The effect of increasing power when grooving using phacoemulsification

PURPOSE

To determine optimal power settings on the Centurion Vision System during the grooving step in cataract surgery.

METHODS

Intact porcine lenses hardened by formalin and placed in a chamber designed to simulate the anterior chamber of the eye were used to test longitudinal power at 40%, 70%, and 100% and torsional power at 0%. Flow rate was set at 40 mL/min. Vacuum was set at 400 mmHg, intraocular pressure was set at 50 mmHg, and a balanced phacoemulsification tip with a 20 degree tip and a 30 degree bevel was used. Efficiency (time to groove the lens in half) was determined.

RESULTS

Increasing longitudinal power from 40% to 70% increased efficiency by 28% (P<0.05), and by 32% (P<0.05) when increasing longitudinal power from 40% to 100%. There was no statistically significant increase in efficiency from 70% to 100%.

CONCLUSION

For the tested variables, a longitudinal power of 70% was determined to be most efficient during the grooving step of cataract surgery for equivalent 3-4+ nuclei. Further increases in power demonstrated no statistically significant improvement in efficiency.

Effect of high vacuum and aspiration on phacoemulsification efficiency and chatter using a transversal ultrasound machine

PURPOSE

To examine the role of high vacuum and aspiration settings on efficiency using a transversal ultrasound (US) machine.

SETTING

John A. Moran Eye Center Laboratory, University of Utah, Salt Lake City, Utah, USA.

DESIGN

Experimental study.

METHODS

Porcine lens nuclei were incubated in formalin for 2 hours and then cut into 2.0 mm cubes. Phacoemulsification was performed using the Whitestar Signature machine. Settings were bottle height 50 cm, on-time 6 milliseconds, and off-time 6 milliseconds. One hundred percent power was used for all 240 runs. Tested parameters were aspiration of 50 mL/min and 60 mL/min and vacuum of 500, mm Hg, 600 mm Hg, and 650 mm Hg.

RESULTS

With continuous US, increasing aspiration from 50 mL/min to 60 mL/min significantly increased efficiency (23%). Increasing vacuum from 500 mm Hg to 650 mm Hg and from 600 mm Hg to 650 mm Hg significantly increased efficiency (20.2% and 13.6%, respectively). Higher vacuum and aspiration parameters did not influence the incidence of chatter events. In the micropulse US group, there was no significant efficiency increase with increasing vacuum or aspiration levels. There was a significant efficiency increase of continuous over micropulse US at an aspiration setting of 60 mL/min and vacuum settings of 600 mm Hg and 650 mm Hg.

CONCLUSIONS

As aspiration and vacuum increased, efficiency increased under continuous transverse US. No significant efficiency improvement occurred at high aspiration and vacuum settings under micropulse US. At 60 mL/min aspiration and more than 600 mm Hg vacuum, continuous power was significantly more efficient than micropulse transverse US.

Optimum on-time duty cycle for a transversal ultrasound machine

PURPOSE

To evaluate the optimum on-time setting for the most efficient removal of lens fragments using micropulse ultrasound (US) and Ellips FX transversal US in the Whitestar Signature Pro phacoemulsification machine.

SETTING

John A. Moran Eye Center Laboratories, University of Utah, Salt Lake City, Utah, USA.

DESIGN

Experimental study.

METHODS

Porcine lens nuclei were soaked in formalin for 2 hours and cut into 2.0 mm cubes. The US machine was used with a bent 0.9 mm phaco tip and a 30-degree bevel. The off time was set to 6 milliseconds (ms) and the on time varied from 4 to 10 ms in 1 ms increments. Efficiency (time for fragment removal) and chatter (number of times the fragment bounced from the tip) were measured.

RESULTS

A linear incremental increase in efficiency was observed between 4 ms and 6 ms. The most statistically significant efficiency was achieved with an on time of 6 ms. On times shorter than 6 ms were significantly less efficient (P = .05). Greater on times (7 to 10 ms) did not result in a significant difference in efficiency (P = .72), but did appear to have more chatter events when comparing on-time settings of 7 to 10 ms with 4 to 6 ms (P = .02).

CONCLUSIONS

With micropulse transversal US, 6 ms of on time was as efficient as longer on times. To maximize phacoemulsification efficiency and minimize chatter events, an on time of 6 ms is recommended.

Effect of increasing flow when grooving during phacoemulsification

PURPOSE

To determine optimum flow settings on the Centurion Vision System during the grooving step in cataract surgery.

SETTING

John A. Moran Eye Center Laboratory, University of Utah, Salt Lake City, Utah, USA.

DESIGN

Experimental study.

METHODS

Intact porcine lenses hardened by formalin and placed in a chamber designed to simulate the anterior chamber of the eye were used to test flow rate settings at 20 mL/min, 40 mL/min, and 60 mL/min. Vacuum was set at 400 mm Hg, longitudinal power at 80%, torsional power at 80%, and intraocular pressure at 50 mm Hg. A balanced phaco tip with a 20-degree tip and a 30-degree bevel was used. Efficiency (time to groove the lens in half) was determined.

RESULTS

Increasing flow from 20 to 40 mL/min during grooving increased efficiency by 17% (P = .05), with no significant improvement shown at 60 mL/min.

CONCLUSIONS

A flow rate of 40 mL/min was determined to be most efficient during the grooving step of cataract surgery. Further increases in flow rate showed no statistically significant improvement in efficiency, and with only 17% improvement flow rates less than 40 mL/min might be almost as efficient and might be safer.

Effect of chamber stabilization software on efficiency and chatter in a porcine lens model

PURPOSE

To evaluate the effects of the use of programmable chamber stabilization software (Chamber Stabilization Environment) settings on efficiency and chatter in a porcine lens model.

SETTING

John A. Moran Eye Center Laboratory, University of Utah, Salt Lake City, Utah, USA.

DESIGN

Experimental study.

METHODS

Porcine eyes were dissected and the lenses extracted. The lenses were then hardened and processed for the experiment. Phacoemulsification of the lens fragments was performed with the Whitestar Signature Pro with the Whitestar handpiece and a 0.9 mm straight Dewey tip with a 30-degree bevel. All arms of the study were run in peristaltic mode with 50 mL/minute aspiration, 100 cm bottle height, and on 100% power. The chamber stabilization software setting was used for each of the 4 study arms with a maximum vacuum of 500 mm Hg. Arm 1 included 20 runs with the up time set to 2000 milliseconds. Arm 2 was performed with similar settings but with an up time of 0 millisecond. Arms 3 and 4 were run with up times of 1000 milliseconds and 500 milliseconds, respectively.

RESULTS

The mean efficiency time of each run was as follows: 0 millisecond = 1.4 seconds, 500 milliseconds = 0.95 seconds, 1000 milliseconds = 0.88 seconds, 2000 milliseconds = 0.93 seconds. When compared with 0 millisecond, each of the other arms were significantly faster. Chatter events were comparable between the study arms.

CONCLUSION

The chamber stabilization software does not decrease efficiency when compared with full vacuum on if at least 500 milliseconds of up time is maintained.

The Effect of Pulsing on Transverse Ultrasound Efficiency and Chatter

PURPOSE

To evaluate the effects of micropulse, long pulse, and continuous ultrasound on transverse ultrasound using Abbott Medical Optics' (AMO) WhiteStar Signature Pro with the Ellips FX handpiece.

DESIGN

In vitro laboratory study.

METHODS

This study was conducted at the John A. Moran Eye Center Laboratory, University of Utah, Salt Lake City, Utah, USA. Porcine lenses were hardened in formalin for 2 hours and equilibrated in basic salt solution (BSS) over a 24-hour period. The lenses were then cubed in 2.0 × 2.0-mm pieces. These pieces were stored in BSS until the time of experimentation. The AMO WhiteStar Signature Pro machine (Abbott Medical Optics) with the Ellips FX handpiece and a 0.9-mm bent Dewey tip with a 30-degree bevel (Microsurgical Technology Inc) were used for phacoemulsification. Three runs of 20 lenses each were performed, measuring efficiency and chatter. Transverse ultrasound varied in the 3 runs and included continuous, 6 ms on/off micropulse, and 50 ms on/off long pulse.

RESULTS

Micropulse was more efficient than long pulse by 43% (P = .00003) and continuous by 42% (P = .000387). There were also less chatter events with micropulse than with long-pulse and continuous ultrasound. However, this difference did not reach significance.

CONCLUSION

The 6 ms on and 6 ms off micropulse transverse 3-dimensional ultrasound is more efficient and produces fewer chatter events than both long-pulse and continuous ultrasound.

Comparison of Vacuum and Aspiration on Phacoemulsification Efficiency and Chatter Using a Monitored Forced Infusion System

PURPOSE

To evaluate the effect of vacuum and aspiration rates on phacoemulsification efficiency and chatter using a monitored forced infusion system.

DESIGN

In vitro animal study.

METHODS

SETTING

John A. Moran Eye Center, University of Utah, Salt Lake City, Utah.

PROCEDURES

Formalin-soaked porcine lenses were divided into 2 mm cubes (tip diameter, 0.9 mm). Vacuum levels were tested at 200, 300, 400, and 500 mm Hg; aspiration rates at 20, 35, and 50 mL/min. Torsional power was set at 60% and intraocular pressure at 50 mm Hg.

RESULTS

Increasing vacuum increased efficiency regardless of aspiration rates (R(2) = 0.92; P = .0004). Increasing aspiration further increased efficiency when vacuum was at 400 and 500 mm Hg (P = .004 for 20 vs 35 mL/min, P = .0008 for 35 vs 50 mL/min). At 200 and 300 mm Hg, efficiency only improved when increasing aspiration to 35 mL/min (P < .0001 with 20 vs 35 + 50 mL/min). Chatter improved with increasing vacuum, up to 400 mm Hg (P = .003 for 200 vs 300 mm Hg and P = .045 for 300 vs 500 mm Hg). A similar trend of improved chatter was seen with increasing levels of aspiration.

CONCLUSIONS

Vacuum improved efficiency up to 500 mm Hg independent of flow. Flow has an additive effect on efficiency through 50 mL/min, when vacuum is at 400 mm Hg or higher, and only up to 35 mL/min at vacuums less than 400 mm Hg. Chatter correlated with both vacuum and flow such that increasing either parameter decreases chatter, up to 400 mm Hg with vacuum.

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.

Effect of pulsing ultrasound on phacoemulsification efficiency

PURPOSE

To evaluate pulse type technology used to remove lens fragments during phacoemulsification.

SETTING

John A. Moran Eye Center Laboratories, University of Utah, Salt Lake City, Utah, USA.

DESIGN

Experimental study.

METHODS

Lens nuclei soaked in 10 mL of 10% neutral buffered formalin for 2 hours were placed in 10 mL of balanced salt solution. Lenses were cut into 2 mm × 2 mm cubes; no more than 36 hours later, cubes were randomly selected for testing. Two aspiration and 2 vacuum settings were assessed at moderate- and high-flow and vacuum (30 mL/min and 300 mm/Hg, low-flow vacuum; 50 mL/min and 500 mm/Hg, high-flow vacuum), with continuous 50 milliseconds on and off (long pulse) and 6 milliseconds on and off (micropulse) ultrasound.

RESULTS

There was a significant difference in efficiency favoring micropulse compared with combined long pulse and continuous pulse in high-flow vacuum at 80% power (P = .018) and between combined long pulse and continuous pulse versus micropulse in high-flow vacuum at 20% power (P = .019). Low-flow vacuum micropulse was more efficient than continuous (19.7%) (P < .0001) and long pulse (22.7%) (P < .0001). Continuous and long pulses were not significantly different from one other. There was a significant difference in chatter rates between high-flow vacuum and low-flow vacuum when all results were compared (P < .0001), with no additional significant differences found.

CONCLUSION

Micropulse technology was better than continuous and long pulse at moderate but not high-flow and vacuum settings. At the higher setting, chatter was observed less often, with all modalities more efficient than the lower setting.

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.

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.

Safety Profile of Venturi Versus Peristaltic Phacoemulsification Pumps in Cataract Surgery Using a Capsular Surrogate for the Human Lens

PURPOSE

To compare the risk of capsular rupture of the human lens during cataract surgery from contact by phacoemulsification needles using different vacuum pumps, ultrasound modalities, and contact angles.

DESIGN

Experimental laboratory investigation.

METHODS

The John A. Moran Eye Center, University of Utah, Salt Lake City, Utah, was the setting for this study. A Signature (Abbott Medical Optics, Inc) phacoemulsification machine was used in peristaltic and Venturi vacuum modes with transversal and micropulsed ultrasound. Contact was made with a capsular surrogate to achieve tip occlusion or tip contact only. Breakage rates were calculated by analyzing the capsular surrogate under a surgical microscope.

RESULTS

Venturi and peristaltic pump modes had similar risk of capsular rupture, regardless of whether the data were analyzed with tip occlusion data included (44.2% peristaltic vs 40.2% Venturi, P = .047) or excluded from the analysis (66.3% peristaltic vs 60.3% Venturi, P = .013). Transversal ultrasound was significantly more likely to cause capsular rupture than micropulsed ultrasound (69.8% vs 56.8%, P < .0001). Tip contact was significantly more likely than tip occlusion to cause capsular rupture (63.3% vs 0%, P < .0001).

CONCLUSIONS

There is no significant difference in risk of capsular rupture using Venturi rather than peristaltic vacuum pumps, while transversal seemed to increase the risk when compared to micropulsed ultrasound. Tip occlusion is not a risk factor for capsular rupture, as all breaks in the capsular surrogate occurred with tip contact.

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 (R(2) = 0.41, P = .046), which was more substantial between 30% and 100% power (R(2) = 0.71, P = .004). The mean number of chatter events did not differ significantly between power settings (R(2) = 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.