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REFERENCES 1. Yeoh R. Practical differences between 3 femtosecond phaco laser platforms [letter]. J Cataract Refract Surg 2014; 40:510– 511; reply by KE Donaldson, 510–511 2. Schultz T, Conrad-Hengerer I, Hengerer FH, Dick HB. Intraocular pressure variation during femtosecond laser–assisted cataract surgery using a fluid-filled interface. J Cataract Refract Surg 2013; 39:22–27 3. Chylack LT Jr, Wolfe JK, Singer DM, Leske MC, Bullimore MA, Bailey IL, Friend J, McCarthy D, Wu S-Y, for the Longitudinal Study of Cataract Study Group. The Lens Opacities Classification System III. Arch Ophthalmol 1993; 111:831–836. Available at: http://www.chylackinc.com/LOCS_III/LOCS_III_Certification_ files/LOCS_III_Reprint_pdf.pdf. Accessed May 14, 2014 4. Lubahn JG, Kankariya VP, Yoo SH. Grid pattern delivered to the cornea during femtosecond laser–assisted cataract surgery. J Cataract Refract Surg 2014; 40:496–497 5. Schultz T, Dick HB. Suction loss during femtosecond laser– assisted cataract surgery. J Cataract Refract Surg 2014; 40:493–495 €m M. 6. Behndig A, Montan P, Stenevi U, Kugelberg M, Lundstro One million cataract surgeries: Swedish National Cataract Register 1992–2009. J Cataract Refract Surg 2011; 37:1539–1545 7. Dick HB, Schultz T. On the way to zero phaco. J Cataract Refract Surg 2013; 39:1442–1444 8. Donaldson KE. Reply to letter by Yeoh R. Practical differences between 3 femtosecond phaco laser platforms. J Cataract Refract Surg 2014; 40:510–511 9. Grewal DS, Basti S. Intraoperative vertical gas breakthrough during clear corneal incision creation with the femtosecond cataract laser. J Cataract Refract Surg 2014; 40:666–670 10. Schultz T, Joachim SC, Kuehn M, Dick HB. Changes in prostaglandin levels in patients undergoing femtosecond laser-assisted cataract surgery. J Refract Surg 2013; 29:742–747 11. Dick HB, Gerste RD. Plea for femtosecond laser pre-treatment and cataract surgery in the same room. J Cataract Refract Surg 2014; 40:499–500

Reply : Dr. Yeoh brings to light some interesting thoughts on suction time and docking time during femtosecond laser–assisted cataract surgery. In our case report, we described that while the lens fragmentation pattern was being delivered to the patient's lens, the patient suddenly moved and disengaged from the patient interface, resulting in the fragmentation pattern being placed in the temporal cornea.1 Fortunately, this complication is rare at our institution; we have not had similar cases since we began using the laser 18 months ago. Regarding procedure times, we have evaluated the time it takes to complete femtosecond laser–assisted cataract surgery at our institution, but we did not routinely record suction or docking times.2 However, to limit the procedure time in all cases, surgeons in our practice tailor the lens fragmentation pattern to the density and type of cataract. Thus, with the event being so rare, having limited data on suction and docking times, and since the

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event discussed in our case report was secondary to the patient suddenly moving during the procedure, it is uncertain whether our complication was related to suction time or docking time.dJordon G. Lubahn, MD REFERENCES 1. Lubahn JG, Kankariya VP, Yoo SH. Grid pattern delivered to the cornea during femtosecond laser–assisted cataract surgery. J Cataract Refract Surg 2014; 40:496–497 2. Lubahn JG, Donaldson KE, Culbertson WW, Yoo SH. Operating times of experienced cataract surgeons beginning femtosecond laser-assisted cataract surgery. In press, J Cataract Refract Surg.

Pain during dominant-side or nondominant-side phacoemulsification In their recent article, Aslankurt et al.1 describe differences in pain and cooperation among patients having dominant-side or nondominant-side phacoemulsification under topical and intracameral anesthesia. They report significantly higher visual analogue scale (VAS) pain scores and reduced cooperation scores in patients having surgery on the dominant side than in those having surgery on the nondominant side. Aslankurt et al. also report that 40 of 78 patients (51.3%) rated their pain severity as zero. Since the VAS scores range from 0 (no pain) to 10 (unbearable pain), this suggests that the pain scores from this group of patients do not follow a normal distribution but are skewed toward the lower end of the scale, as one would expect for pain experienced during phacoemulsification. Similar observations have been made in earlier studies, in which the median VAS score was either 1 or 0.2 It has been reported that while the t test is more powerful under relatively symmetric distributions, it may not be as accurate for comparing data with nonnormal distributions. Instead, a nonparametric test should be used in these situations.3,4 It would be interesting to know whether the differences in pain scores between the dominant-side and nondominant-side groups are still observed when nonparametric tests (such as the Wilcoxon rank sum test) are used in this analysis. It would also be useful to know the relative proportions of various pain scores between the 2 groups; in particular, the frequency of a score of 0 (no pain) in both groups and whether these are significantly different. The observation that women had higher VAS scores than men in this study is interesting. While many earlier studies of pain encountered during cataract surgery did not compare pain scores among men and women, a double-masked randomized controlled trial of 506 patients reported that on multivariate

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analysis, women were more likely to experience pain than men (54.3% versus 43.6%, odds ratio 1.56, PZ.016).2 Aslankurt et al.1 have explored several possible explanations for this observation in their paper. Regardless of the precise reasons, this information is important since cataract surgeons need to identify patients at risk for experiencing pain to plan additional measures to alleviate it. In summary, this paper has provided useful new information on the factors affecting pain encountered during phacoemulsification. We agree with the authors that these factors should be kept in mind when evaluating the success of measures to relieve pain. Colin S.H. Tan, MB BS, MMed (Ophth), FRCSEd(Ophth) Joel C. Chan Wei Kiong Ngo, MB BS Kai Xiong Cheong, MB BS Singapore Dr. Tan receives research funding from the National Healthcare Group Clinician Scientist Career Scheme Grant (Code: CSCS/12005) and also receives travel support from Bayer (South East Asia) Pte Ltd. (Code: R). REFERENCES 1. Aslankurt M, Aslan L, Bas‚kan AM, Aksoy A, Silay E, Yıldız H. Pain and cooperation in patients having dominant-side or nondominant-side phacoemulsification. J Cataract Refract Surg 2014; 40:199–202 2. Tan CSH, Fam H-B, Heng W-J, Lee H-M, Saw S-M, Au Eong K-G. Analgesic effect of supplemental intracameral lidocaine during phacoemulsification under topical anaesthesia: a randomised controlled trial. Br J Ophthalmol 2011; 95:837–841 3. Bridge PD, Sawilowsky SS. Increasing physicians’ awareness of the impact of statistics on research outcomes: comparative power of the t-test and Wilcoxon Rank-Sum test in small samples applied research. J Clin Epidemiol 1999; 52:229–235 4. McCluskey A, Lalkhen AG. Statistics II: central tendency and spread of data. Contin Educ Anaesth Crit Care Pain 2007; 7:127–130. Available at: http://ceaccp.oxfordjournals.org/content/ 7/4/127.full.pdf. Accessed April 9, 2014

Reply : We appreciate the incisive analysis of our article, particularly for calling attention to a point that we missed. When we reevaluated with the Levene test, we noticed that the distribution of VAS scores was not normal. However, the Wilcoxon rank sum test, which was suggested by Drs. Tan et al., may not be appropriate for this series. The Mann-Whitney U test may be more appropriate because of the single measurements that were made in 2 separate groups. When the data were reevaluated with this test, VAS scores were again found to be higher in dominantside surgeries (PZ.009, Mann-Whitney U test). The

Table 1. Proportions of various pain scores between the 2 groups. VAS Score Dominant Side (n, %) Nondominant Side (n, %) 0 1 2 Total

32 (69.6) 10 (21.7) 4 (8.7) 46 (100)

30 (93.8) 0 (0) 2 (6.3) 32 (100)

VAS Z visual analogue scale

relative proportions of various pain scores in the 2 groups are shown in Table 1.dMurat Aslankurt, MD, Lokman Aslan, MD, Adnan Aksoy, MD, Murat Ozdemir, MD

Visual experience of the cataract patient after surgery I recently had the experience of being the patient who has cataract surgery and afterward noticed in detail some interesting changes in color vision that have implications for surgical technique. As a retired ophthalmologist who once performed cataract operations and witnessed the many revolutionary changes in technique since the introduction of intraocular lenses, I have also seen significant improvements in operating microscope systems and ancillary equipment. My own surgery lasted only 10 minutes. Although I remember concerns expressed for decades about the need to minimize macular light exposure from the operating microscope,1,2 I did not think about that until after my experience as a patient. I think my postoperative visual experience should be of great interest to other surgeons. Following my outpatient surgery, I walked straight home (quite impossible to have imagined only 40 years ago). On my walk home, I noted that the color of traffic signals appeared different and both red and green signals were yellowish, indicating a loss of blue cone response. This worried me, but in approximately 2 weeks, my blue sensitivity returned and traffic signals were their expected coloration. Sperling et al.1 showed more than 40 years ago that trained primates exposed to monochromatic light of different wavelengths temporarily lost red and green cone response after intense red or green exposures, but the blue cone response could be permanently suppressed after sufficiently high blue light exposures. I feel fortunate that my blue cone sensitivity returned. Some operating microscope illumination systems have either a fixed or insertable yellow (blue-violet–

J CATARACT REFRACT SURG - VOL 40, JULY 2014

Pain during dominant-side or nondominant-side phacoemulsification.

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