Pain during phacoemulsification with and without cryoanalgesia

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their assertion that the Barrett calculator is the best of the 3 examined. Michael J. Goggin, FRCSI(Ophth) Adelaide, South Australia REFERENCES 1. Abulafia A, Barrett GD, Kleinmann G, Ofir S, Levy A, Marcovich AL, Michaeli A, Koch DD, Wang L, Assia EI. Prediction of refractive outcomes with toric intraocular lens implantation. J Cataract Refract Surg 2015; 41:936–944 2. Alpins NA. A new method of analyzing vectors for changes in astigmatism. Cataract Refract Surg 1993; 19:524–533 3. Reinstein DZ, Archer TJ, Randleman JB. JRS standard for reporting astigmatism outcomes of refractive surgery [editorial]. J Refract Surg 2014; 30:654–659; erratum 2015; 31:129 4. Goggin M, Patel I, Billing K, Esterman A. Variation in surgically induced astigmatism estimation due to test-to-test variations in keratometry. J Cataract Refract Surg 2010; 36:1792–1793 5. Alpins N, Ong JKY, Stamatelatos G. New method of quantifying corneal topographic astigmatism that corresponds with manifest refractive cylinder. J Cataract Refract Surg 2012; 38:1978–1988

Reply : We thank Dr. Goggin for his interest in our paper comparing the refractive outcome using different methods to predict toric IOL power in patients with preexisting astigmatism having cataract surgery. As Dr. Goggin mentions, the key parameter examined was the difference vector between the predicted astigmatic result and the actual postoperative astigmatic result described as the error in the predicted residual astigmatism. As a vector, both the magnitude and axis of the error must be considered, as shown in the double-plot diagrams and numerically as the centroid value representing the mean vector error in the entire group. The actual axis of the implanted IOL was measured, and the postoperative keratometry was considered to eliminate axis misalignment and incisional SIA as confounding factors in this analysis. Thus, Dr. Goggin's suggestion that a toric IOL power prediction can be “perfectly accurate” in the presence of IOL misalignment is not relevant. The magnitude of the cylinder error, regardless of the axis error, is clinically significant, and this was also provided in our paper in terms of the mean/ median absolute values as suggested by Dr. Goggin as well as the percentage of patients predicted to be within G0.50 diopter (D), 0.75 D, and 1.00 D of the predicted residual astigmatism. The tendency to overestimate or underestimate toric IOL power is best represented by the double-angle plot and centroid values, as discussed above, representing both the magnitude and the axis of the error.1 The SDs for each centroid values in Table 2 were calculated according to Holladay at el.1

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We thank the Dr. Goggin for pointing out a reference-numbering error (12 instead of 13) for the formulas that were used to predicted net corneal astigmatism assessment for the Baylor nomogram. These formulas are presented in the study by Koch et al.2 (Figure 2). The Baylor nomogram aims to leave the eye with a small with-the-rule refractive astigmatism. This aim is not included in those formulas. We appreciate Dr. Goggin's suggestion that the CorT3 might be a useful value to consider in our analysis. This is certainly an interesting approach. However, the CorT value was validated only in respect to manifest refraction in phakic eyes and hence includes lenticular astigmatism. Before it is applied as a value that represents corneal astigmatism alone, we believe that it has to be validated in a setting in which the influence of noncorneal factors is excluded. In our opinion, the additional terminology suggested by Dr. Goggin does not add to the analysis in communicating the results in our study. dAdi Abulafia, MD, Graham D. Barrett, MD, Douglas D. Koch, MD, Li Wang, MD, PhD, Ehud I. Assia, MD REFERENCES 1. Holladay JT, Moran JR, Kezirian GM. Analysis of aggregate surgically induced refractive change, prediction error, and intraocular astigmatism. J Cataract Refract Surg 2001; 27:61–79 2. Koch DD, Ali SF, Weikert MP, Shirayama M, Jenkins R, Wang L. Contribution of posterior corneal astigmatism to total corneal astigmatism. J Cataract Refract Surg 2012; 38:2080–2087 3. Alpins N, Ong JKY, Stamatelatos G. New method of quantifying corneal topographic astigmatism that corresponds with manifest refractive cylinder. J Cataract Refract Surg 2012; 38:1978– 1988

Pain during phacoemulsification with and without cryoanalgesia We read with interest the article by Coelho et al.1 that reported no significant difference in the mean pain score during phacoemulsification between eyes that received topical anesthesia only and those that received topical anesthesia with cryoanalgesia. Although the authors checked for a normal distribution of the pain scores, the mean pain scores reported were 26.0 and 21.3 on a scale of 0 to 100, with small standard deviations. This is consistent with the results in earlier studies of pain during phacoemulsification that reported pain scores on the lower end of the visual analog scale.2,3 It would be interesting to know whether significant difference in pain scores would have been observed had the median scores been compared using nonparametric tests instead. Because the authors sought to determine whether a lower temperature reduces the severity of pain,

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maintenance of the irrigating solution at 4 C is imperative to properly test the hypothesis. We are curious to know whether steps were taken to maintain the temperature once the irrigating solution was removed from the refrigerator and whether this was actively monitored. Because the surgeries took an average of 11 to 12 minutes, it is possible that the temperature of the irrigating solution was affected by the ambient room temperature as the surgery progressed. This might diminish the potential analgesic effects of cryoanalgesia. Also of interest is whether the sample-size calculation and statistical analysis took into account the possible interactions between various systemic and ocular confounders that are known to affect the pain experienced during phacoemulsification. It has been reported that pain experienced during surgery varies with sex,2,4 with age,2 and among patients having surgery to the second eye.2,3 Although the sample size might have been sufficient to detect a difference in the mean pain score, as the author reported, it would be ideal to design a study that has a sufficiently large sample to allow multivariate analysis, which would account for the above-mentioned confounders. We commend the authors for their study of various means to reduce the pain patients experience during phacoemulsification, which is something all ophthalmologists strive for during surgery. Other effective methods include the use of intracameral lidocaine to supplement the effects of the topical anesthesia.2,5 This might be a simple and cost-effective method of providing a more comfortable surgical experience to our patients. Louis W. Lim, MB BS Colin S.H. Tan, MB BS, MMed(Ophth), FRCSEd (Ophth) Singapore REFERENCES 1. Coelho RP, Biaggi RH, Jorge R, Rodrigues Mde L, Messias A. Clinical study of pain sensation during phacoemulsification with and without cryoanalgesia. J Cataract Refract Surg 2015; 41:719–723 2. Tan CSH, Fam HB, Heng WJ, Lee HM, Saw SM, Au Eong KG. Analgesic effect of supplemental intracameral lidocaine during phacoemulsification under topical anaesthesia: a randomised controlled trial. Br J Ophthalmol 2011; 95:837–841 3. Jiang L, Zhang K, He W, Zhu X, Zhou P, Lu Y. Perceived pain during cataract surgery with topical anesthesia: a comparison between first-eye and second-eye surgery. J Ophthalmol 2015 article ID 383456. Available at: http://downloads.hindawi.com/ journals/joph/2015/383456.pdf. Accessed July 20, 2015  ska-Olszewska I, Synder A. Factors 4. Omulecki W, Laudan affecting patient cooperation and level of pain perception during phacoemulsification in topical and intracameral anesthesia. Eur J Ophthalmol 2009; 19:977–983 5. Gupta SK, Kumar A, Kumar D, Agarwal S. Manual small incision cataract surgery under topical anesthesia with intracameral lignocaine: study on pain evaluation and

surgical outcome. Indian J Ophthalmol 2009; 57:3–7. Available at: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC 2661525/?reportZprintable. Accessed July 20, 2015

Reply : We are pleased that Drs. Lim and Tan appreciated our work and made their comments, which surely improve on our research. Although we reported only the results from the parametric test in our article, we had also compared our sample using a nonparametric test. The results are similar: P Z .1926, Wilcoxon signed-rank test. In fact, the lower number of patients with higher pain scores with cold solution (8/25) might be an indicator of the higher probability of lower pain scores if the infusion solution were colder. On the other hand, the small, and not statistically significant, mean difference in pain scores between cold solution versus roomtemperature solution also indicates that this might be clinically irrelevant. We made this observation in our discussion (page 722). Also, we made clear to the reader that a larger number of patients reported a lower pain score with cryoanalgesia. We did not monitor infusion temperature during surgery. Other authors consider it very unlikely that room temperature could markedly change the solution temperature during the 15 minutes of surgery. Moreover, for each surgery, 500 mL of a balanced salt solution was taken from a 4 C refrigerator in the operating room. Considering a room temperature of 23 C for 15 minutes, we would expect only a small increase in temperature. Sample-size estimation was based on the standard deviation found for pain sensation scores during cataract surgery in a similar environment,1 meaning that all these variables were automatically taken into account. The inclusion of a larger number of patients could have led to statistical significance but could have detected smaller differences. The minimum difference in the pain score that could have been detected with our sample was 7.1, which we considered reasonable. In addition, the highest difference between pain scores was approximately 30, either higher for cold solution or higher for room-temperature solution (Figure 1, page 722), indicating that the cold temperature increased the discomfort in some patients to a degree similar that it decreased pain in other patients. We appreciate that Drs. Lim and Tan mention the use of intracameral lidocaine to reduce pain during phacoemulsification. We agree that this has been used as an alternative for topical anesthesia alone; however, it has drawbacks, such as the potential

J CATARACT REFRACT SURG - VOL 41, AUGUST 2015