509
LETTERS
REFERENCES 1. Carones F, Vigo L, Scandola E, Vacchini L. Evaluation of the prophylactic use of mitomycin-C to inhibit haze formation after photorefractive keratectomy. J Cataract Refract Surg 2002; 28:2088–2095 2. Leccisotti A. Mitomycin-C in hyperopic photorefractive keratectomy. J Cataract Refract Surg 2009; 35:682–687 3. Thomas KE, Brunstetter T, Rogers S, Sheridan MV. Astigmatism: risk factor for postoperative corneal haze in conventional myopic photorefractive keratectomy. J Cataract Refract Surg 2008; 34:2068–2072 4. Hersh PS, Schein OD, Steinert R; Summit Photorefractive Keratectomy Phase III Study Group. Characteristics influencing outcomes of excimer laser photorefractive keratectomy. Ophthalmology 1996; 103:1962–1969 5. Seiler T, Holschbach A, Derse M, Jean B, Genth U. Complications of myopic photorefractive keratectomy with the excimer laser. Ophthalmology 1994; 101:153–160
Intracameral moxifloxacin injection to prevent endophthalmitis In their article on intracameral injection of moxifloxacin in the prevention of endophthalmitis, Matsuura et al.1 report 8 cases of endophthalmitis in the control group of 15 958 and 3 cases of endophthalmitis in the treatment group of 18 794. They report an incidence of 0.051% (1 in 1955) in the control group and of 0.015% (1 in 6265) in the treatment group, suggesting a statistically significant difference (P Z .037). I would like to point out that there are inaccuracies in their statistical analysis, some of which are significant. First, the incidence in the control group should be 0.050% (8/15 958 Z 0.05013%, not 0.051%) and in the treatment group, 0.016% (3/18 794 Z 0.01596%, not 0.015%), albeit these are small errors. Second, when comparing the incidences in the groups, the authors use the 1-tailed chi-square test, which is inappropriate for 2 reasons: (1) The authors assume that the treatment group can do no worse than the control group. (2) The incidences of 8 and 3 are too small to be used with the chi-square test. The more appropriate test is the 2-tailed Fisher exact testA; with this test, the P value is 0.1267 (2-tailed), indicating no statistically significant difference between the groups. Third, the odds ratio (OR) (the odds of developing endophthalmitis in the control group to that in the treatment group) is 3.1416, indicating that there is a 3-fold decrease in the incidence of endophthalmitis with intracameral moxifloxacin, consistent with the authors' claim. Last, however, the 95% confidence interval of the OR is from 0.7539 to 18.3876, which includes 1, confirming that the difference between the groups is not statistically insignificant. In conclusion, based on the data reported, the authors should indicate that their study fails to show
a statistically significant difference in the incidence of endophthalmitis between the control and the treatment groups, even though there is a 3-fold decrease in the incidence of endophthalmitis with intracameral moxifloxacin in their study. Sheridan Lam, MD Lombard, Illinois, USA REFERENCE 1. Matsuura K, Miyoshi T, Suto C, Akura J, Inoue Y. Efficacy and safety of prophylactic intracameral moxifloxacin injection in Japan. J Cataract Refract Surg 2013; 39:1702–1706
OTHER CITED MATERIAL A. The R Project for Statistical Computing. Available at: http://www. r-project.org/. Accessed January 7, 2014
Reply : We agree with Dr. Lam that 0.051% and 0.015% should be 0.050% and 0.016%, respectively. In addition, the 2-tailed Fisher exact test may be more appropriate. We now have data from another 2 institutions (Table 1). The OR of developing endophthalmitis in the control group to that of the treatment group is 3.584 (interval 0.860 to 20.977). It still fails to show a statistically significant difference between the control and the treatment group (P Z .064, 2-tailed Fisher exact test). Postoperative endophthalmitis is a rare complication of cataract surgery. Therefore, studies evaluating the efficacy of any prophylactic measure to reduce the actual risk for endophthalmitis would require a large number of patients and are difficult to perform. The total number of cases in our 21 institutions is approximately 12 000 per year. We would like to resurvey after a few years and reevaluate the efficacy and safety of intracameral moxifloxacin. dKazuki Matsuura, MD, Teruyuki Miyoshi, MD, Chikako Suto, MD, Junsuke Akura, MD, Yoshitsugu Inoue, MD
Table 1. Incidence of postoperative endophthalmitis before and after moxifloxacin administration in the original study plus 2 additional institutions. Cataract Endophthalmitis Prophylaxis Surgeries (n) Cases (n) Without IC MFLX With IC MFLX
Infection Rate
17485
8
1/2186 (0.046%)
23501
3
1/7834 (0.013%)
IC Z intracameral; MFLX Z moxifloxacin
J CATARACT REFRACT SURG - VOL 40, MARCH 2014
LETTERS
REFERENCES 1. Carones F, Vigo L, Scandola E, Vacchini L. Evaluation of the prophylactic use of mitomycin-C to inhibit haze formation after photorefractive keratectomy. J Cataract Refract Surg 2002; 28:2088–2095 2. Leccisotti A. Mitomycin-C in hyperopic photorefractive keratectomy. J Cataract Refract Surg 2009; 35:682–687 3. Thomas KE, Brunstetter T, Rogers S, Sheridan MV. Astigmatism: risk factor for postoperative corneal haze in conventional myopic photorefractive keratectomy. J Cataract Refract Surg 2008; 34:2068–2072 4. Hersh PS, Schein OD, Steinert R; Summit Photorefractive Keratectomy Phase III Study Group. Characteristics influencing outcomes of excimer laser photorefractive keratectomy. Ophthalmology 1996; 103:1962–1969 5. Seiler T, Holschbach A, Derse M, Jean B, Genth U. Complications of myopic photorefractive keratectomy with the excimer laser. Ophthalmology 1994; 101:153–160
Intracameral moxifloxacin injection to prevent endophthalmitis In their article on intracameral injection of moxifloxacin in the prevention of endophthalmitis, Matsuura et al.1 report 8 cases of endophthalmitis in the control group of 15 958 and 3 cases of endophthalmitis in the treatment group of 18 794. They report an incidence of 0.051% (1 in 1955) in the control group and of 0.015% (1 in 6265) in the treatment group, suggesting a statistically significant difference (P Z .037). I would like to point out that there are inaccuracies in their statistical analysis, some of which are significant. First, the incidence in the control group should be 0.050% (8/15 958 Z 0.05013%, not 0.051%) and in the treatment group, 0.016% (3/18 794 Z 0.01596%, not 0.015%), albeit these are small errors. Second, when comparing the incidences in the groups, the authors use the 1-tailed chi-square test, which is inappropriate for 2 reasons: (1) The authors assume that the treatment group can do no worse than the control group. (2) The incidences of 8 and 3 are too small to be used with the chi-square test. The more appropriate test is the 2-tailed Fisher exact testA; with this test, the P value is 0.1267 (2-tailed), indicating no statistically significant difference between the groups. Third, the odds ratio (OR) (the odds of developing endophthalmitis in the control group to that in the treatment group) is 3.1416, indicating that there is a 3-fold decrease in the incidence of endophthalmitis with intracameral moxifloxacin, consistent with the authors' claim. Last, however, the 95% confidence interval of the OR is from 0.7539 to 18.3876, which includes 1, confirming that the difference between the groups is not statistically insignificant. In conclusion, based on the data reported, the authors should indicate that their study fails to show
a statistically significant difference in the incidence of endophthalmitis between the control and the treatment groups, even though there is a 3-fold decrease in the incidence of endophthalmitis with intracameral moxifloxacin in their study. Sheridan Lam, MD Lombard, Illinois, USA REFERENCE 1. Matsuura K, Miyoshi T, Suto C, Akura J, Inoue Y. Efficacy and safety of prophylactic intracameral moxifloxacin injection in Japan. J Cataract Refract Surg 2013; 39:1702–1706
OTHER CITED MATERIAL A. The R Project for Statistical Computing. Available at: http://www. r-project.org/. Accessed January 7, 2014
Reply : We agree with Dr. Lam that 0.051% and 0.015% should be 0.050% and 0.016%, respectively. In addition, the 2-tailed Fisher exact test may be more appropriate. We now have data from another 2 institutions (Table 1). The OR of developing endophthalmitis in the control group to that of the treatment group is 3.584 (interval 0.860 to 20.977). It still fails to show a statistically significant difference between the control and the treatment group (P Z .064, 2-tailed Fisher exact test). Postoperative endophthalmitis is a rare complication of cataract surgery. Therefore, studies evaluating the efficacy of any prophylactic measure to reduce the actual risk for endophthalmitis would require a large number of patients and are difficult to perform. The total number of cases in our 21 institutions is approximately 12 000 per year. We would like to resurvey after a few years and reevaluate the efficacy and safety of intracameral moxifloxacin. dKazuki Matsuura, MD, Teruyuki Miyoshi, MD, Chikako Suto, MD, Junsuke Akura, MD, Yoshitsugu Inoue, MD
Table 1. Incidence of postoperative endophthalmitis before and after moxifloxacin administration in the original study plus 2 additional institutions. Cataract Endophthalmitis Prophylaxis Surgeries (n) Cases (n) Without IC MFLX With IC MFLX
Infection Rate
17485
8
1/2186 (0.046%)
23501
3
1/7834 (0.013%)
IC Z intracameral; MFLX Z moxifloxacin
J CATARACT REFRACT SURG - VOL 40, MARCH 2014
