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Back to Journal »Clinical Ophthalmology» Volume 15
Optimizing the tip diameter in phacoemulsification of lens of different sizes: an in vitro study
Authors Ramshekar A, Heczko J, Bernhisel A, Barlow Jnr W, Zaugg B, Olson R, Pettey J
Published on November 17, 2021, the 2021 volume: 15 pages 4475-4484
DOI https://doi.org/10.2147/OPTH.S333903
Single anonymous peer review
Editor approved for publication: Dr. Scott Fraser
Aniket Ramshekar, 1, 2, Joshua Heczko, 1 Ashlie Bernhisel, 1 William Barlow Jnr, 1 Brian Zaugg, 1 Randall Olson, 1 Jeff Pettey 1 1 Department of Ophthalmology and Visual Sciences, John A. Moran Eye Center, University of Utah , Salt Lake City, UT, 84132, USA; 2 University of Utah School of Medicine, Salt Lake City, Utah, 84132, USA, USA Phone +1 801-581-2352 Fax +1 801-581-3357 Email [email protected ] Purpose: We evaluated the efficiency and chatter of two lens sizes, three tip sizes, and two ultrasound (US) methods for phacoemulsification. Method: After soaking the pig lens nucleus in formalin, it is divided into 2.0mm or 3.0mm cubes. We used the continuous torsion US system to collect efficiency and flutter data for 30-degree bending 19 G, 20 G, and 21 G tips; and straight 19 G, 20 G, and 21 G tips with a micro-pulse longitudinal US system. Result: The average removal time of the 3.0 mm lens cube is always higher than the 2.0 mm lens cube. A statistically significant difference was observed between the micropulse longitudinal US using 2.0 mm cubes and 3.0 mm cubes and the 19 G and 21 G tips of continuous transverse US using 2.0 mm lens cubes and 3.0 mm cubes. We did not observe any significant difference between the 19 G and 20 G needle tips in any cube size in any US system. However, we noticed the same trend in the two cube sizes for the two US methods; the 19 G tip performed better than the 20 G and 21 G tips. Conclusion: Regardless of the lens size, the 19 G needle is the most effective, with the fewest outliers and the smallest standard deviation. Keywords: cataract, flutter, efficiency, tip diameter, vacuum
Phacoemulsification (phaco) allows the cataract lens to be safely removed before the replacement lens is inserted. However, the technology needs to continue to be optimized to improve surgical results. In this study, we compared two lens sizes, three ultrasonic tips, and two ultrasound (US) methods. Our team believes that there may be a relationship between lens fragment size and tip aperture, which may limit the efficiency advantage of larger apertures.
Using the technology we developed earlier, we cut the pig lens into 2.0 and 3.0 mm cubes. We determined the efficiency and flutter of the 30-degree bend 19 G tip and the 20 G and 21 G tips by micro-pulse longitudinal ultrasound or continuous torsional ultrasound.
Consistent with our hypothesis, we found that for each ultrasound change and all tips, the average removal time using a 3.0 mm lens cube was longer. We observed that the 20 G tip has no efficiency advantage compared to the 19 G tip, especially the 3.0 mm cube. For continuous lateral US, we found that the 19 G tip is more effective than the 20 G tip. We noticed that compared to the 2.0 mm and 3.0 mm cubes using 20 and 21 G tips, there was significantly more jitter when removing the 3.0 mm cube using the 19 G needle in the micropulse longitudinal US. Interestingly, we noticed that the 3.0 mm cube using the 19 G needle in the micropulse longitudinal US increases the flutter.
Our findings on these previously unknown relationships are important to establish the best balance between efficiency, wound size, and safety.
Phacoemulsification (phaco) technology is used in modern cataract surgery to emulsify and aspirate the lens of the eye, rinse with a balanced salt solution instead of pumped fluid, and maintain the integrity of the anterior chamber. 1 In order to successfully complete a cataract surgery, it is important to select the best settings to balance jet and ultrasound (US) power, proper phaco tip size and design.
A previous study in our laboratory evaluated the effect of phaco tip angle and phaco tip diameter on the efficiency of removing 2 mm lens fragments. 2 However, the average cataract lens is about 5 mm before and after, and about 9 mm at the equator; 3 is divided into quadrants, and the resulting lens fragments are about 4-5 mm in diameter. To date, there have been no peer-reviewed publications documenting the effect of tip diameter on the echocardiographic efficiency of lenses of different sizes. Therefore, the use of a pig 3 mm cubic lens in this study will not only try to simulate the size of clinically relevant lens fragments, but will also test the idea that the efficiency and tremor will be significantly different when using various phaco tip sizes to emulsify larger fragments. Micro-pulse longitudinally under US power supply.
We assume that needles with larger apertures will be more effective at the specified vacuum level because they increase the surface area. In addition, we assume that using a needle with a larger aperture will result in increased material consumption per cycle of tip movement; regardless of the phaco setting, this will result in a reduction in the removal time of the 2mm and 3mm lens cubes. Since the selected phaco parameters have a great impact on efficiency and flutter, we used the most effective combination found in the previously reported research. 2,4-31
This in vitro study does not include human subjects or animals, nor does it require the approval of the Institutional Review Board and Institutional Animal Care and Use Committee of the University of Utah.
The swine lens obtained from Visiontech, Inc. (Sunnyvale, Texas, USA) was prepared as described in the previous paper. 2,5-7 After dissection within 48 hours of arrival, each lens nucleus is in 10 mL of 10% neutral buffered formalin. Subsequently, all cell nuclei were placed in 10 mL of Balanced Salt Solution (BSS) for 24 hours; this process increased the uniformity of formalin hardening. In the lens cutting device, the same person cuts each lens into a cube of 2.0 mm or 3.0 mm to reduce the variability of the size of lens fragments. 2,4-7 These cubes are stored in a humid chamber filled with BSS until the experiment is carried out no more than 24 hours after the lens is cut. The density and behavior of these pig lenses are comparable to those of human cataracts during ultrasound surgery. 5 In order to randomly select cubes in each experiment, all lens cubes are placed in a container and mixed frequently.
Whitestar machines (Abbott Medical Optics, Inc. Johnson & Johnson Vision [J&J], Santa Ana, California, USA) were used for these studies. We have selected micro-pulse longitudinal US and continuous lateral US after determining the most effective setting for the 2 mm cube. 2,4,5,32 Vertical US is 50% power, micropulse 6 ms on time period and 12 ms off time period. Horizontal US is set to 50% continuous power. Both US models use 50 cm bottle height and 40 mL/min flow rate, and 550 mm Hg vacuum. In addition, both methods use a peristaltic pump setting, allowing independent suction and level control, as described earlier. 2 US and vacuum are kept at their maximum settings, and the full pedal is turned on.
To draw meaningful conclusions between our two lens fragment models, we used the Ellips FX mobile phone (J&J), whose tip is similar to the tip used in our previous 2mm porcine lens model study. 2,4-7 In this study, we used two US mode measuring heads of 19 G, 20 G or 21 G. However, the tip used during the continuous transverse US mode has a 30-degree bend, while the tip used during the micropulse longitudinal US mode is straight and has no bend.
We define efficiency as the number of seconds the US uses to remove lens fragments, while flutter is defined as the amount of lens fragments ejected from the tip. The comparison is consistent with the previously described method. 2,4,5 Place a randomly selected cube lens in our rubber chamber filled with BSS. After the pedal is depressed and the tip is blocked by lens fragments, the pedal is fully depressed to activate the US. The stopwatch records the time interval from the beginning of the US to the complete removal of the debris. If the cube falls off the tip of the phaco at any time during the US, the stopwatch stops. Any movement is considered a chattering event. Whenever the particle moves out of the tip, depress the pedal again to draw a vacuum until it is sucked into the tip. After the particles re-occlude the tip, fully depress the pedal to the US setting, and we restart the timing process so that the flutter delay time can be distinguished from the total particle removal time.
After the average efficiency time, the standard deviation (SD) is calculated. Efficiency times that differ from the average by more than 2 standard deviations are designated as outliers and taken from the data set. Our rationale for excluding these data points is based on previous studies in which we observed cases of tremor that caused the emulsification time to be long enough that they distort the results. 2,4,6,7,23 Therefore, we deleted these abnormal data points from all analyses to best explain our experimental results.
We calculated the corrected mean and SD, and used the paired Student’s t-test to compare the efficiency time between the tip diameters of each US change or multivariate regression to evaluate the predictive phacoemulsification performance assessed by removal time or flutter event Variable; significance is set at P <0.05. Use Stata-17 software (StataCorp LLC, College Station, TX, USA) for analysis.
Regardless of the size of the lens fragments, all American systems increase the lens removal time as the tip size decreases (Figure 1). Use 2.0 mm cube (2.0 seconds ± 1.26 [SD] vs. 3.1 seconds ± 1.84 [SD]; P=0.04) (Figure 1A) and 3.0 mm lens cube (6.8 seconds ± 3.62 [SD] and 11.4 seconds ± 5.61 [SD] ; P=0.005) (Figure 1B), and continuous lateral US (1.2 seconds ± 0.51 [SD] and 1.8 seconds ± 0.84 [SD] using 2.0 mm cubes; P=0.01) (Figure 1C) and 3.0 mm lens cubes ( 4.0 seconds ± 1.77 [SD] and 6.3 seconds ± 2.79 [SD]; P=0.005) (Figure 1D). In addition, the use of 2.0 mm (2.0 sec ± 1.20 [SD] and 3.1 sec ± 1.84 [SD]; P = 0.03) micropulse longitudinal US system has a statistically significant reduction in emulsification time between 20 and 21 G tips And 3.0 mm lens cube (7.1 seconds ± 4.10 [SD] vs 11.4 seconds ± 5.61 [SD]; P=0.01). Regardless of the US system, no statistically significant difference was found in the removal time of the 2 mm lens between the 19 G and 20 G tips. However, compared with the 20 G tip (4.0 seconds ± 1.77 [SD] vs. 5.8 seconds ± 2.88 [SD]), the emulsification time of 3 mm lens fragments with a 19 G tip in a continuous transverse ultrasound system is statistically significant Decrease; P=0.02) (Figure 1D). Combining all US studies, regardless of the US system used, the average lens removal time of a 3mm lens cube is significantly longer than that of a 2mm lens cube (P<0.0001). In addition, regardless of the size of the lens fragments and the US system, the 19 G tip has the most effective removal time. Then, we used the removal times of two lens cube sizes for three pinholes, micropulse longitudinal test (Table 1) and continuous lateral test (Table 2) (excluding outliers) to generate a multivariate regression model. To generate this model, we treat the phacoemulsification system as a binary variable by assigning a value of 0 for the micropulse longitudinal setting and a value of 1 for the continuous lateral setting. This model accounts for approximately 50% of the variance and includes the following variables: echocardiographic settings, pinhole diameter, and lens size (Table 3). The most important predictor of removal time is lens size (P<0.001). Table 1 Timetable for phacoemulsification and flutter measurement using 2 mm and 3 mm lens cubes and micro-pulse longitudinal ultrasonic modalities and various apertures: 19 G, 20 G, 21 G 2 Ultrasound using 2 mm and 3 mm lenses Emulsification and flutter measurement time. Cubes with continuous transverse ultrasonic modes and various apertures: 19 G, 20 G, 21 G Table 3 The final multivariate regression model (related variables, removal time) Figure 1 2 mm or 3 mm pig The average removal time of complete phacoemulsification compares the lens model between two phacoemulsification systems. The average removal time is plotted as a function of tip diameter from (A) micropulse longitudinal US using a 2 mm porcine lens cube, (B) micropulse longitudinal US using a 3 mm porcine lens cube, and (C) using a 2 mm continuous lateral US lens cube, and (D) continuous transverse US using 3 mm lens cube (two-sample t-test is not adjusted for flutter). Error bars represent the standard error of the mean.
Table 1 Time for phacoemulsification and flutter measurement using 2 mm and 3 mm lens cubes, micro-pulse longitudinal ultrasonic modalities and various apertures: 19 G, 20 G, 21 G
Table 2 Phacoemulsification time and flutter measurement using 2 mm and 3 mm lens cubes and continuous transverse ultrasonic modalities and various apertures: 19 G, 20 G, 21 G
Table 3 The final multivariate regression model (dependent variable, removal time)
Figure 1 Comparison of the average removal time of two phacoemulsification systems for complete phacoemulsification of a 2 mm or 3 mm porcine lens model. The average removal time is plotted as a function of tip diameter from (A) micropulse longitudinal US using a 2 mm porcine lens cube, (B) micropulse longitudinal US using a 3 mm porcine lens cube, and (C) using a 2 mm continuous lateral US lens cube, and (D) continuous transverse US using 3 mm lens cube (two-sample t-test is not adjusted for flutter). Error bars represent the standard error of the mean.
Regardless of the tip diameter, there was no statistically significant difference in flutter between when 2 mm lens fragments were emulsified in micropulse longitudinal ultrasound and when 3 mm lens fragments were emulsified in continuous transverse ultrasound (Figure 2). However, when using the 19 G tip, a statistically significant increase in flutter events was observed when the 3 mm lens cube was emulsified in the micropulse longitudinal US setting compared to the 2 mm lens cube (P = 0.02). The flutter events of the three pinholes used in the micropulse longitudinal test (Table 1) and the continuous transverse test (Table 2), excluding outliers, are used to generate a regression model to predict the possibility of flutter events. In order to generate this model, we treat the flutter event as a binary variable. When we do not observe a flutter event, we assign a value of 0, and when we observe one or more flutter events, we assign a value of 1. We also treat the phacoemulsification system as a binary variable by assigning a value of 0 for the longitudinal direction of the micropulse and a value of 1 for the continuous transverse direction. The model only accounts for about 6% of the variance and includes the following variables: echocardiogram settings, pinhole diameter, and lens size (Table 4). The most important predictor of flutter events is lens size (P<0.01). Table 4 The final multivariate regression model (related variables, flutter events) Figure 2 The effect of tip size on the number of flutter events for 2 mm and 3 mm lens cubes. The average removal time is plotted as a function of the number of flutter events for a given tip diameter, from (A) micropulse longitudinal US using a 2 mm porcine lens cube, (B) micropulse longitudinal US using a 3 mm porcine lens cube, ( C) Continuous lateral US using a 2 mm lens cube, and (D) Continuous lateral US using a 3 mm lens cube. Error bars represent the standard error of the mean.
Table 4 The final multivariate regression model (dependent variables, Chatter events)
Figure 2 The effect of tip size on the number of flutter events for 2 mm and 3 mm lens cubes. The average removal time is plotted as a function of the number of flutter events for a given tip diameter, from (A) micropulse longitudinal US using a 2 mm porcine lens cube, (B) micropulse longitudinal US using a 3 mm porcine lens cube, ( C) Continuous lateral US using a 2 mm lens cube, and (D) Continuous lateral US using a 3 mm lens cube. Error bars represent the standard error of the mean.
The different tip diameters and the ability to manipulate vacuum, suction, and irrigation flow rates allow users to customize settings for optimal lens removal. The Poiseuille equation shows that the flow rate is proportional to the 4th power of the tube radius. Small changes in pore size can cause significantly large flow changes. In order to maintain the flow rate with a smaller bore needle, the pump will work harder to maintain the flow rate. 1 creates a potential rate limiting step for the smaller bore tip. In addition, as the size of the fragments increases, more lens material may need to be removed by the echocardiographic tip. In summary, these limitations make needles with smaller apertures less effective in removing larger debris and denser cataracts.
Another variable in phacoemulsification is the ability to hold debris through vacuum. The vacuum is conditionally proportional to the square of the aperture radius of the system, and a higher vacuum level corresponds to the improved efficiency in our previous study. 6,8,22-24 Therefore, it should be beneficial to increase the tip size, because the vacuum pair accelerates the removal of lens particles through the compressive force exerted on the component, thereby ensuring that the component is in contact with the tip during US delivery. However, when inadvertent contact with fragile ocular tissue is more likely to be secondary to increased post-occlusion surges, extreme levels of vacuum pose risks.
In our previous work on the tip hole, we found that the 20 G tip has a statistically significant improvement in debris removal compared to the 21 G tip. Compared with the 20 G or 21 G tip, the 19 G tip has no significant advantages; however, the data shows a trend that the 20 G tip is better than the 19 G tip. 2 We assume that there may be a relationship between the size of the debris and the tip aperture, which may limit the efficiency advantage cube using the larger aperture tip of the 2 mm lens. This theory is the driving force behind this research work. The current research confirms our theory that using a 20 G tip does not see an advantage over a 19 G tip, especially in terms of phaco efficiency, using a larger 3 mm lens cube. In addition, when using a 3 mm cube, the 19 G tip is more effective than the 20 G tip using continuous transverse US. In summary, our results show that when removing larger lens fragments, a tip with a larger aperture has a greater advantage in the efficiency of echocardiography.
The data presented in this article indicate that the trend of 3mm and 2mm lens fragments is similar. We did see that the difference in the 3 mm cube from the 19 G needle to the 20 G needle is much larger than the same difference in the 2 mm lens cube, which really supports our original hypothesis. The main difference is that the duration required to remove the 3 mm lens cube is significantly longer compared to the 2 mm cube. Considering that the lens material to be emulsified is 3.4 times larger, this is not surprising. In fact, the difference in time ratio reflects the size of the lens. This finding supports clinical practice to further reduce the energy consumption of the lens through shredding or other mechanical techniques without worrying about the size of the lens fragments.
Interestingly, compared to the 19 G operation with 2 mm fragments and the 3 mm cube size with 20 and 21 G tips, the flutter event that occurs when the 3 mm lens cube is removed using the 19 G needle in the micropulse longitudinal US Obviously more. Evaluation of the remaining lens fragments after vitrectomy for phacoemulsification found that the vast majority of retained fragments are at least 1/3 the size of the lens nucleus, while smaller lens fragments are rare. 33 The data of this study indicate that the largest lens fragment aperture size combined with larger lens fragments produces greater repulsion in the linear longitudinal phaco, which may explain why the larger lens fragments are retained and cause postoperative complication. For a long time, both clinically and in our previous work, 2,4-7 have noticed that longitudinal forces can cause flutter events. Previously, it was not known whether the size of the tip and lens fragments are important variables that affect the efficiency of ultrasound contrast.
The use of continuous transverse ultrasound is similar but not identical to the results observed with micropulse longitudinal ultrasound. For 2 mm parts, as the needle size decreases, the removal time increases (ie 19 G <20 G <21 G), there is no statistically significant difference between 19 G and 20 G or 20 G and 21 G difference. However, we did find a significant difference between the 19 G and 21 G needles. This is similar to our previous observation that the 0.9 mm tip is more efficient than the 0.7 mm tip. 2
A similar pattern was seen when the 3mm lens was removed. The highest efficiency is when the needle with the largest diameter is used, and the efficiency of 19 G is significantly higher than that of 20 G. This finding was unexpected considering that the 3mm film-19 G experiment demonstrated the significant flutter events observed using micropulse longitudinal US. Another unexpected finding occurred in the 2 mm-19 G continuous lateral operation, which showed a large number of flutter events compared to all other lateral operations using a 2 mm lens. Similarly, we observe a flutter event pattern that depends on tip size, fragment size, and US morphology. Although the clinical relevance of these findings is uncertain, they reinforce the previously unknown and unpredictable nature of phaco variables for flutter events.
Although this study does not intend to directly compare micropulse longitudinal and continuous transverse US, it is worth noting that the latter is more effective on all parameters. However, additional research is needed to confirm this for other machine settings. Finally, our series may show statistically significant differences, powering the study by providing more runs for each setting, thereby increasing the efficiency of larger needle sizes. However, the trend remains consistent with previous work and variable fragment sizes.
The limitations of our study include the potential difference between sclerosing porcine lens and human cataract. We believe that our previous work has associated our experimental lens with more than 3-4 human cataracts. 5 Other limitations include that this study is an in vitro study. In a clinical setting, considering the variability of fragments encountered during surgery, it is impossible to study the effect of any phacoemulsification parameters on fragment size.
Overall, our data supports the view that further mechanical destruction of the lens before using phaco to remove debris is beneficial in clinical settings using larger diameter needles; this may be related to femtosecond laser-assisted cataracts Surgery is related to technology, such as phaco cutting.
In summary, for relatively small and large lens fragments, phaco with a larger tip diameter is more effective. Understanding these previously unknown relationships between the variables tested here is an important step in determining the balance between removal efficiency, wound size, and tissue safety.
BSS, balanced salt solution; Johnson & Johnson, Johnson & Johnson Vision; lens, phacoemulsification; SD, standard deviation; the United States, ultrasound.
The data supporting the results reported in the manuscript can be found on hive.utah.edu (https://hive.utah.edu/concern/datasets/sn009x76k).
Since no human subjects were involved, it was not approved by the Institutional Review Board of the University of Utah.
Susan Shulman assisted in writing and preparing the manuscript.
This research was supported in part by an unrestricted grant from the Blindness Prevention Research Corporation of New York City, New York, USA to the Department of Ophthalmology and Visual Sciences, University of Utah, Salt Lake City, Utah, USA.
Dr. Olson is a member of the board of directors of Perceive Bio and a member of the scientific advisory board of Perfect Lens. Dr. Jeff Pettey reports a consulting agreement from Lensar in addition to the submitted work. Other authors report no other conflicts of interest in this work.
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