Comparison of phaco-chop, divide-and-conquer, and stop-and-chop phaco techniques in microincision coaxial cataract surgery

ARTICLE

Comparison of phaco-chop, divide-and-conquer, and stop-and-chop phaco techniques in microincision coaxial cataract surgery Juwan Park, MD, PhD, Hae ri Yum, MD, Man Soo Kim, MD, PhD, Andrew R. Harrison, MD, Eun Chul Kim, MD, PhD

PURPOSE: To compare the outcomes of coaxial microincision cataract surgery (MICS) performed with 3 phacoemulsification techniques (phaco-chop, divide-and-conquer, and stop-and-chop) according to cataract density. SETTING: Bucheon St. Mary’s Hospital, College of Medicine, Catholic University of Korea, Seoul, South Korea. DESIGN: Prospective randomized clinical trial. METHODS: Eyes with nuclear density from grade 2 to 4 were randomly subdivided into 3 groups (phaco-chop, divide-and-conquer, and stop-and-chop). Intraoperative measurements included ultrasound time (UST), mean cumulative dissipated energy (CDE), and balanced salt solution use. Clinical measurements included preoperative and 1 day, 1 month, and 2 month postoperative corrected distance visual acuity, central corneal thickness, and endothelial cell count. RESULTS: Intraoperative measurements showed significantly less UST, CDE, and balanced salt solution use with the phaco-chop technique than with the divide-and-conquer and stop-and-chop techniques in the grade 4 cataract density group (P<.05). The percentage of endothelial cell loss was significantly lower in the phaco-chop group than in the divide-and-conquer and stop-andchop groups in the grade 4 cataract density group 2 months after cataract surgery (P<.05). CONCLUSIONS: All 3 techniques may be effective for coaxial MICS in mild and moderate cataracts. However, in eyes with hard cataract having coaxial MICS, the phaco-chop technique can be more effective for lens removal, with less corneal endothelial damage, than the divide-and-conquer and stop-and-chop techniques. Financial Disclosure: No author has a financial or proprietary interest in any material or method mentioned. J Cataract Refract Surg 2013; -:-–- Q 2013 ASCRS and ESCRS

With advancements in cataract surgery technology, incision size, phacoemulsification energy, and endothelial cell loss have been reduced and phacoemulsification efficiency has been increased.1 Coaxial microincision cataract surgery (MICS) has become a safe and effective technique for performing the procedure.1 Endothelial cell loss was initially increased in MICS, especially in eyes with increased nuclear density, because of increased cumulative dissipated energy (CDE), aspiration time, and volume of balanced salt solution used.2 The intraoperative energy used and ocular damage can be decreased in MICS with the pulse and burst modes compared with the continuous mode for hard cataract.3 Q 2013 ASCRS and ESCRS Published by Elsevier Inc.

Advanced phacoemulsification techniques may also decrease energy use.4 The phaco-chop technique requires lower ultrasound (US) energy for nuclear management than the stop-and-chop technique in dense cataracts; however, it has been reported that the resulting endothelial loss was similar with both techniques in small-incision cataract surgery.4 Several new techniques were introduced to increase the efficiency of phacoemulsification of hard cataract.5,6 To our knowledge, there are no studies comparing MICS phacoemulsification techniques according to cataract density. We compared the outcomes of coaxial MICS performed with 3 phacoemulsification 0886-3350/$ - see front matter http://dx.doi.org/10.1016/j.jcrs.2013.04.033

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COMPARISON OF TECHNIQUES IN MICROINCISION COAXIAL CATARACT SURGERY

Table 1. Preoperative clinical data (15 eyes in each NO group). Phaco-Chop Technique Parameter Mean age (y) Mean CDVA (log MAR) Mean corneal thickness (mm) Mean ECC (cells/mm2) P value*

NO2

NO3

NO4

62.1 G 7.0 0.39 G 0.33 517.4 G 18.5 2655.3 G 233.6 O.05

69.4 G 6.8 0.27 G 0.05 526.1 G 11.0 2632.7 G 215.2 O.05

72.6 G 7.3 0.24 G 0.14 526.3 G 9.0 2560.8 G 236.4 O.05

Means G SD CDVA Z corrected distance visual acuity; ECC Z endothelial cell count; NO Z nucleus opacity *Comparison of 3 phaco techniques in the same nuclear opacity subgroups (Tukey highly significant difference and Duncan tests)

techniques (phaco-chop, divide-and-conquer, and stop-and-chop) according to the cataract density. PATIENTS AND METHODS This prospective randomized study comprised eyes with cataract that were randomly assigned to have phacoemulsification and posterior chamber intraocular lens (IOL) implantation at the Bucheon St. Mary's Hospital between May 2010 and December 2010. The study protocol followed the guidelines of the Declaration of Helsinki and an institutional review board. Patients provided written informed consent after receiving an explanation of the surgical systems used in the study. The eyes were equally randomized according to 3 cataract densities (nuclear opalescence [NO]2, NO3, NO4). Each density group was randomly assigned to have phacoemulsification with the divide-and-conquer technique, phaco-chop technique, or stop-and-chop technique. Exclusion criteria included corneal pathology, pseudoexfoliation, history of ocular trauma, and intraoperative complications such as posterior lens capsule rupture, lens dislocation, and ocular inflammation. Preoperative assessment included corrected distance visual acuity (CDVA), nucleus opacity grading by slitlamp

Submitted: November 30, 2012. Final revision submitted: March 27, 2013. Accepted: April 3, 2013. From the Department of Ophthalmology & Visual Science (Park, Yum, M.S. Kim, E.C. Kim), College of Medicine, Catholic University of Korea, Seoul, South Korea; the Department of Ophthalmology (Harrison), College of Medicine, University of Minnesota, Minneapolis, Minnesota, USA. Supported by National Research Foundation of Korea Grant founded by the Korean Government (2012038648) and Research to Prevent Blindness, New York, New York, USA. Corresponding author: Eun Chul Kim, MD, PhD, Department of Ophthalmology, Bucheon St. Mary’s Hospital, number 2 SosaDong, Wonmi-Ku, Bucheon, Kyungki-Do 420-717, South Korea. E-mail: [email protected].

examination, central corneal thickness (CCT) by US pachymetry, and endothelial cell count (ECC) by specular microscopy. The types of cataract and grades of density were classified preoperatively using the Lens Opacities Classification System III.7

Intraoperative and Postoperative Measurements Intraoperative measurements included total balanced salt solution used, ultrasound time (UST), and mean CDE.8 The postoperative parameters measured at 1 day, 1 month, and 2 months were CDVA, CCT, and ECC.

Phaco Machine Settings Phaco machine settings were identical in all study groups. Microcoaxial phacoemulsification was performed with the Intrepid Infiniti system (Alcon Laboratories, Inc.), which uses torsional US. The height of the infusion bottle was set at 100 cm. The aspiration flow rate was 35 mL/min, and the vacuum level was set at 400 mm Hg.

Surgical Technique Phacoemulsification was performed by the same surgeon (E.C.K.). In all cases, surgery began with a clear incision at a temporal corneal site created with a double-beveled 2.2 mm incision knife (Alcon). Then, the anterior chamber was filled with sodium hyaluronate 1.0% (Hyal Plus). A 5.5 mm continuous curvilinear capsulorhexis was made using an Inamura capsulorhexis forceps (Duckworth & Kent Ltd). Hydrodissection and hydrodelineation were achieved using a balanced salt solution. In all cases, a 0.9 mm flared 45-degree ABS Kelman microtip (Alcon) was used. For the phaco-chop technique, phacoemulsification began with quadrant-removal parameters. After the cortex and epinucleus were aspirated, the phaco tip was buried in the center of the epinucleus with high vacuum. Then, the phaco chopper was inserted through the side-port and placed opposite the main incision at the edge of the nucleus. The chopper was positioned under the lower edge of the capsulorhexis and pulled toward the phaco tip. The 2 instruments were then moved in opposite directions to divide the nucleus into halves. This process was continued for both nuclear halves by rotating them 90 degrees. The phacoemulsification tip was impaled in

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COMPARISON OF TECHNIQUES IN MICROINCISION COAXIAL CATARACT SURGERY

Table 1. (cont.) Divide-and-Conquer Technique

Stop-and-Chop Technique

NO2

NO3

NO4

NO2

NO3

NO4

61.3 G 8.3 0.28 G 0.14 522.7 G 15.6 2644.1 G 305.9 O.05

67.3 G 10.2 0.30 G 0.14 520.8 G 12.4 2530.2 G 343.5 O.05

70.9 G 7.9 0.22 G 0.11 523.7 G 12.5 2633.7 G 303.6 O.05

67.7 G 9.2 0.26 G 0.22 519.2 G 11.6 2519.2 G 278.5 O.05

69.8 G 9.3 0.34 G 0.16 520.9 G 15.8 2697.9 G 304.7 O.05

68.2 G 16.0 0.19 G 0.18 523.5 G 12.4 2480.3 G 267.5 O.05

half the nucleus, and the chopper was used to break this half into 2 smaller fragments, which were then emulsified and aspirated. The procedure was repeated in the other half of the nucleus. For the divide-and-conquer technique, 4 trenches were sculpted (with vacuum set at 0 mm Hg) so the nucleus could be cracked bimanually into 4 segments. The 4 quadrants were emulsified in the capsular bag using increased vacuum (up to 90 mm Hg). The rest of the procedure was similar to that used in the phaco-chop technique. In the stop-and-chop technique, the phacoemulsification probe was used to sculpt a central crater down to 85% of nuclear thickness. After the groove was created, the chopper was inserted into the depth of the crater and the posterior plate of the nucleus was cracked in half by laterally moving the chopper and phacoemulsification probe in opposite directions. After the nucleus was split, phacoemulsification was performed and the nuclear halves were cut into fragments and then emulsified and aspirated, as in the phaco-chop group. Epinucleus and cortex removal was performed with infusion/aspiration cannulas in all groups. After the procedures above, sodium hyaluronate 1% (Healon) was injected into the anterior chamber and a YA60-BBR IOL (Hoya Corp.) was implanted in the capsular bag using a dedicated injector system. In all groups, IOL implantation was performed under the protection of an ophthalmic viscosurgical device (OVD), which was subsequently removed through aspiration. The wound was not sutured.

Central Corneal Thickness The CCT was measured using US pachymetry (SW-1000P, Suoer) preoperatively and 1 and 2 months postoperatively. The pachymeter was precalibrated for all measurements. The CCT was measured with the patient seated upright. A handheld probe was aligned on the central cornea as perpendicularly as possible. Ten readings were obtained and averaged. The same observer took all measurements.

Endothelial Cell Counts The ECC was measured using a noncontact specular microscope (Noncon Robo-CA SP-8000) preoperatively and 1 and 2 months postoperatively. The center method was used for cell counting. Approximately 50 to 60 cells were

counted manually from each photograph in the semiautomatic cell-density algorithm of the microscope. Three central fields were counted, and the average of these counts was used to represent endothelial cell density (ECD) at any timepoint. Endothelial cell loss was evaluated as follows: Endothelial cell loss Z (preoperative cell count postoperative cell count)/(preoperative cell count  100%). One examiner was masked as to which group the images belonged. At each visit, 3 photographs were taken of each eye.

Statistical Analysis All data are expressed as the mean G SD. The Tukey highly significant difference (HSD), Duncan, and independent-samples t tests were used to compare the groups for statistical significance. The analyses were performed using SPSS for Windows software (version 13.0, SPSS, Inc.). A P value less than .05 was considered statistically significant.

RESULTS The study comprised 135 eyes of 135 patients. Each cataract density group (NO2, NO3, NO4) had 45 eyes. In each cataract density group, the first 15 patients had phacoemulsification with the divideand-conquer technique, the next 15 patients with the phaco-chop technique, and the final 15 patients with the stop-and-chop technique. Table 1 shows the characteristics of the patients in each group. There were no statistically significant differences in age, preoperative CDVA, ECD, or CCT between the groups (P!.05). Intraoperative Parameters The UST was significantly less in the NO4 group with the phaco-chop technique than with the divideand-conquer and stop-and-chop techniques (P!.05). The CDE energy and balanced salt solution used in the NO4 group were also significantly less with the

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COMPARISON OF TECHNIQUES IN MICROINCISION COAXIAL CATARACT SURGERY

Table 2. Comparison of UST, CDE, and balanced salt solution use after phacoemulsification between techniques according to cataract density (15 eyes in each NO group). Mean G SD Phaco-Chop Technique Parameter

NO2

NO3

NO4

Divide-and-Conquer Technique NO2

NO3

NO4

Stop-and-Chop Technique NO2

NO3

NO4

UST (s) 17.9 G 10.1 26.8 G 7.4 30.6 G 12.4* 36.1 G 10.6 48.8 G 11.6 55.4 G 16.6 22.9 G 14.1 30.9 G 15.2 48.4 G 15.51 CDE 10.2 G 3.5 12.9 G 4.2 15.1 G 3.8* 12.3 G 4.7 15.7 G 3.7 19.7 G 4.3 14.1 G 5.6 17.5 G 6.4 18.1 G 5.6 Balanced salt 72.2 G 15.6 76.4 G 19.4 82.3 G 22.8* 81.8 G 20.3 84.5 G 21.5 127.9 G 32.1 79.9 G 15.2 82.6 G 16.4 112.0 G 39.7 solution use (mL) CDE Z cumulative dissipated energy; NO Z nuclear opacity; UST Z ultrasound time *P!.05

phaco-chop technique than with the divide-andconquer and stop-and-chop techniques (P!.05). There was no significant difference in effective phacoemulsification time, CDE, or balanced salt solution used in the NO2 and NO3 groups between the phaco techniques (Table 2). Central Corneal Thickness Although there was less change in the CCT in all cataract density groups with the phaco-chop technique than with the divide-and-conquer and stop-and-chop techniques 2 months postoperatively, the difference was not statistically significant (Figure 1).

ECC, 2560.8 G 236.4 cells/mm2 preoperatively and 2427.6 G 212.7 cells/mm2 postoperatively) than with the divide-and-conquer technique (9.1% G 1.2%; mean ECC, 2633.7 G 303.6 cells/mm2 preoperatively and 2394.0 G 245.7 cells/mm2 postoperatively) and the stop-and-chop technique (7.2% G 1.0%; mean ECC, 2480.3 G 267.5 cells/mm2 preoperatively and 2455.5 G 250.5 cells/mm2 postoperatively) in the NO4 group (P!.05). Although the percentage of endothelial cell loss was lower with the phaco-chop technique than with the divide-andconquer and stop-and-chop techniques in the NO2 and NO3 groups, the difference was not significant (Figure 2).

Corneal Endothelial Cell Loss Two months postoperatively, the mean percentage of endothelial cell loss was significantly lower with the phaco-chop technique (5.2% G 0.6%; mean

Corrected Distance Visual Acuity There was an equal and significant increase in logMAR CDVA with the 3 phaco techniques from preoperatively to 2 months postoperatively in the NO2, NO3, and NO4 groups (Table 3).

Figure 1. Postoperative changes of CCT by technique and cataract density (* Z Tukey HSD and Duncan tests).

Figure 2. Postoperative endothelial cell loss by technique and cataract density (* Z Tukey HSD and Duncan tests).

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COMPARISON OF TECHNIQUES IN MICROINCISION COAXIAL CATARACT SURGERY

Table 3. Preoperative and postoperative CDVA (15 eyes in each NO group). Mean CDVA G SD Phaco-Chop Technique Exam Preop 1 d postop 1 mo postop 2 mo postop P value*

Divide-and-Conquer Technique

Stop-and-Chop Technique

NO2

NO3

NO4

NO2

NO3

NO4

NO2

NO3

NO4

0.39 G 0.33 0.85 G 0.18 0.87 G 0.16 0.91 G 0.10 O.05

0.27 G 0.05 0.75 G 0.16 0.78 G 0.12 0.87 G 0.11 O.05

0.24 G 0.14 0.75 G 0.16 0.77 G 0.14 0.85 G 0.09 O.05

0.28 G 0.14 0.75 G 0.28 0.77 G 0.26 0.85 G 0.14 O.05

0.30 G 0.14 0.77 G 0.19 0.78 G 0.18 0.87 G 0.08 O.05

0.23 G 0.11 0.70 G 0.25 0.72 G 0.22 0.85 G 0.14 O.05

0.26 G 0.22 0.71 G 0.29 0.81 G 0.18 0.87 G 0.12 O.05

0.34 G 0.16 0.66 G 0.21 0.73 G 0.15 0.88 G 0.10 O.05

0.19 G 0.18 0.63 G 0.17 0.78 G 0.18 0.86 G 0.12 O.05

CDVA Z corrected distance visual acuity; NO Z nuclear opacity *Comparison of 3 phaco techniques in the same nuclear opacity subgroups (Tukey highly significant difference and Duncan tests)

DISCUSSION Corneal endothelial damage during phacoemulsification can be caused by irrigation flow, turbulence and movement of fluids, presence of air bubbles and free-radical release, and direct trauma caused by the instruments or lens fragments.9 Moreover, the use of longer phacoemulsification time and greater power is believed to cause direct endothelial cell damage.10 More sophisticated instruments, better OVDs, and improvements in IOLs and surgical techniques have decreased iatrogenic trauma.10 The divide-and-conquer technique was introduced to crack the nucleus and facilitate phacoemulsification.11 This technique requires additional phaco energy for sculpting to divide the nucleus before the fragments are emulsified.11 Therefore, different nuclear-chopping techniques were introduced to further decrease postoperative complications. Nagahara introduced the phaco-chop concept in 1993.12 The phaco-chop technique can reduce phaco time and power because manual chopping is used to divide the nucleus into manageable fragments and the only significant use of phaco energy is during fragment emulsification.13 The stop-and-chop technique, introduced by Koch and Katzen,13 begins by creating a central groove that provides space and facilitates separation of the posterior plate. After this, the cracking procedure is stopped and chopping of the remaining parts begins.12 The creation of a central groove using US energy at the beginning of the procedure is the important difference between the phaco-chop technique and the stop-andchop technique.12 Several studies have compared various chopping techniques with standard-incision phacoemulsification. Wong et al.14 used a Legacy system (Alcon) and found a mean phacoemulsification time of 1.2 minutes for the phaco-chop technique and

2.4 minutes for the divide-and-conquer technique. Unlike the divide-and-conquer technique, the phaco-chop technique does not require nuclear sculpting. In addition, the phaco-chop technique tends to direct the US away from the cornea, yet the phaco tip is farther from the posterior capsule than in divide-and-conquer technique.14 This, combined with less zonular stress, may be particularly important when patients have a potential for weak zonular fibers and low endothelial cell counts.14 This, combined with less rotational manipulation of the nucleus, creates less zonular stress and reduces cephalocaudal movement of the phaco tip through a tight section, which may decrease the risk for Descemet membrane detachment. Therefore, it would be expected that the phaco-chop technique would produce fewer ocular complications than the divideand-conquer and stop-and-chop techniques.14 Park et al.4 found that in cataracts with moderate nuclear density, the phaco-chop technique and stopand-chop technique are equally efficacious in cracking the nucleus. However, the US energy consumption was lower (shorter phacoemulsification time and lower phacoemulsification power) with the phaco-chop technique than with the stop-and-chop technique in denser cataracts and the resulting endothelial loss was similar with both techniques. Can et al.12 found that the mean phacoemulsification time was shorter and the phacoemulsification power was lower with the phaco-chop technique than with the stop-and-chop technique. The mean times to achieve maximum vision and to return to preoperative corneal thickness were also shorter with the phaco-chop technique. In this study, we compared the phaco-chop, stopand-chop, and divide-and-conquer techniques in MICS according to cataract density. We found that the stop-and-chop and divide-and-conquer

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techniques required a longer phacoemulsification time, higher phacoemulsification power, and more balanced salt solution than the phaco-chop technique in hard cataracts (P!.05). We found no significant difference in postoperative parameters, such as CDVA and CCT, between the 3 phacoemulsification techniques with all nuclear opacities; however, the percentage of corneal endothelial cell loss was lower with the phaco-chop technique than with the stopand-chop and divide-and-conquer techniques in eyes with hard cataract (P!.05). However, other studies found no statistically significant difference in endothelial cell loss between the phaco-chop and stop-and-chop techniques4,15 and or between the phaco-chop and divide-and-conquer techniques in standard-incision cataract surgery.16 Endothelial cell damage after MICS and standardincision cataract surgery has been evaluated, and incision size was not found to be a direct factor influencing endothelial cell loss.17 Phaco time, US energy, mechanical trauma by instruments, corneal manipulation, fluid turbulence, and sleeveless phacoemulsification have been reported as being the main factors in endothelial cell damage.17 In contrast, Park et al.4 found that the ECC loss at 6 months was significantly higher in the microcoaxialincision group than in the standard-incision group (PZ.048). Mahdy et al.2 also found statistically significant endothelial cell loss with microcoaxial phacoemulsification, especially with increased nuclear hardness. With increasing cataract density, there was a need for more time and increased amounts of balanced salt solution to remove the lens. This was associated with fluid turbulence in the anterior chamber and consequently more endothelial cell loss.2 It is thought that corneal endothelial cells are more susceptible to damage with MICS than with standard-incision phacoemulsification, especially in eyes with hard cataract. We hypothesize that the phaco-chop technique may decrease the damage to corneal endothelial cells more than the stop-andchop and divide-and-conquer techniques, especially in microcoaxial phacoemulsification for hard cataract. To our knowledge, this is the first study comparing 3 phacoemulsification techniques using MICS. We found that the stop-and-chop and divide-andconquer techniques were as safe as the phaco-chop technique in MICS in eyes with mild to moderate cataract. However, for hard cataract, the phaco-chop technique can decrease intraoperative parameters and postoperative ECC loss more than the stop-andchop and divide-and-conquer techniques. The limitation of this study is that the results are short term. A long-term study is needed.

WHAT WAS KNOWN  In standard-incision cataract surgery, there is no statistically significant change in endothelial cell loss between the phaco-chop and stop-and-chop techniques or between the phaco-chop and divide-and-conquer techniques. WHAT THIS PAPER ADDS  In coaxial MICS, the phaco-chop technique can decrease intraoperative parameters compared with the stop-andchop and divide-and-conquer techniques in hard cataracts using coaxial MICS.  In coaxial MICS, the phaco-chop technique can decrease postoperative corneal endothelial cell loss compared with the stop-and-chop and divide-and-conquer techniques in hard cataracts.

REFERENCES 1. Lee K-M, Kwon H-G, Joo C-K. Microcoaxial cataract surgery outcomes: comparison of 1.8 mm system and 2.2 mm system. J Cataract Refract Surg 2009; 35:874–880 2. Mahdy MAES, Eid MZ, Mohammed MA-B, Hafez A, Bhatia J. Relationship between endothelial cell loss and microcoaxial phacoemulsification parameters in noncomplicated cataract surgery. Clin Ophthalmol 2012; 6:503–510. Available at: http:// www.ncbi.nlm.nih.gov/pmc/articles/PMC3334211/pdf/opth-6503.pdf. Accessed April 19, 2013 3. Kim EC, Byun YS, Kim MS. Microincision versus small-incision coaxial cataract surgery using different power modes for hard nuclear cataract. J Cataract Refract Surg 2011; 37:1799–1805 4. Park JH, Lee SM, Kwon J-W, Kim MK, Hyon JY, Wee WR, Lee JH, Han YK. Ultrasound energy in phacoemulsification: a comparative analysis of phaco-chop and stop-and-chop techniques according to the degree of nuclear density. Ophthalmic Surg Lasers Imaging 2010; 41:236–241 5. Hwang HS, Kim EC, Kim MS. Drill-and-crack technique for nuclear disassembly of hard nucleus. J Cataract Refract Surg 2010; 36:1627–1630 6. Kim HK. Decrease and conquer: phacoemulsification technique for hard nucleus cataracts. J Cataract Refract Surg 2009; 35:1665–1670 7. Chylack LT Jr, Wolfe JK, Singer DM, Leske MC, Bullimore MA, Bailey IL, Friend J, McCarthy D, Wu S-Y; Longitudinal Study of Cataract Study Group. The Lens Opacities Classification System III. Arch Ophthalmol 1993; 111:831–836 8. Fine IH, Packer M, Hoffman RS. Use of power modulations in phacoemulsification: choo-choo chop and flip phacoemulsification. J Cataract Refract Surg 2001; 27:188–197 9. Linebarger EJ, Hardten DR, Shah GK, Lindstrom RL. Phacoemulsification and modern cataract surgery. Surv Ophthalmol 1999; 44:123–147 10. Pirazzoli G, D’Eliseo D, Ziosi M, Acciarri R. Effects of phacoemulsification time on the corneal endothelium using phacofracture and phaco chop techniques. J Cataract Refract Surg 1996; 22:967–969 11. Gimbel HV. Divide and conquer nucleofractis phacoemulsification: development and variations. J Cataract Refract Surg 1991; 17:281–291

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€ u _ Takmaz T, C‚akıcı F, Ozg €l M. Comparison of Nagahara 12. Can I, phaco-chop and stop-and-chop phacoemulsification nucleotomy techniques. J Cataract Refract Surg 2004; 30:663–668 13. Koch PS, Katzen LE. Stop and chop phacoemulsification. J Cataract Refract Surg 1994; 20:566–570 14. Wong T, Hingorani M, Lee V. Phacoemulsification time and power requirements in phaco chop and divide and conquer nucleofractis techniques. J Cataract Refract Surg 2000; 26:1374–1378 15. Vajpayee RB, Kumar A, Dada T, Titiyal JS, Sharma N, Dada VK. Phaco-chop versus stop-and-chop nucleotomy for phacoemulsification. J Cataract Refract Surg 2000; 26:1638–1641 16. Storr-Paulsen A, Norregaard JC, Ahmed S, Storr-Paulsen T, Pedersen TH. Endothelial cell damage after cataract surgery: divide-and-conquer versus phaco-chop technique. J Cataract Refract Surg 2008; 34:996–1000

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17. Mastropasqua L, Toto L, Vecchiarino L, Di Nicola M, Mastropasqua R. Microcoaxial torsional cataract surgery 1.8 mm versus 2.2 mm: functional and morphological assessment. Ophthalmic Surg Lasers Imaging 2011; 42:114–124

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First author: Juwan Park, MD, PhD Department of Ophthalmology & Visual Science, College of Medicine, Catholic University of Korea, Seoul, South Korea