gator, Consultant, Honoraria; QLT, Inc: Consultant, Honoraria; Digi- sight: Advisory Board, Honoraria. The author of the original article declined to reply.
Correspondence Bayer Healthcare: Grants, Consultant; Carl Zeiss Meditec: Grants, Consultant, Speaker. K.B.F.–Genentech: Advisory Board, Investigator, Honoraria; Regeneron Pharmaceuticals, Inc: Advisory Board, Investigator, Consultant, Honoraria; QLT, Inc: Consultant, Honoraria; Digisight: Advisory Board, Honoraria. The author of the original article declined to reply.
References 1. Monés J, Biarnés M, Trindade F. Hyporeflective wedgeshaped band in geographic atrophy secondary to age-related macular degeneration: an underreported finding. Ophthalmology 2012;119:1412–9. 2. Hendrickson AE, Yuodelis C. The morphological development of the human fovea. Ophthalmology 1984;91:603–12. 3. Hunter DG, Patel SN, Guyton DL. Automated detection of foveal fixation by use of retinal birefringence scanning. Appl Opt 1999;38:1273–9. 4. Otani T, Yamaguchi Y, Kishi S. Improved visualization of Henle fiber layer by changing the measurement beam angle on optical coherence tomography. Retina 2011;31:497–501. 5. Lujan BJ, Roorda A, Knighton RW, Carroll J. Revealing Henle’s fiber layer using spectral domain optical coherence tomography. Invest Ophthalmol Vis Sci 2011;52:1486 –92.
Macular Hole and Choroidal Thickness Dear Editor: We read with great interest and attention the recent article from Zeng et al1 regarding the choroidal thickness in both eyes of patients with unilateral idiopathic macular hole. They concluded that choroidal thickness was thinner in eyes affected with idiopathic macular hole and in fellow unaffected eyes, in comparison with age- and gender-matched control eyes. Their observations partly confirm the findings previously reported by Reibaldi et al2 using the same study design. Although the measurements seem to be accurate and the results interesting, we feel that the statistical procedure used by the authors is not robust enough to support their conclusion because of several shortfalls in the statistical analysis; therefore, the interpretation of the results could be misleading. Indeed, several basic statistical considerations were omitted in this study, which could affect the significance of the results. The authors conducted an age- and gender-matched case-control study and they verified in Table 1 that no differences exist between the 3 groups in terms of age, gender, or refractive error; however, they did not compare the axial length, which is known to be among the most important confusion factors for the interpretation of the foveal thickness.3 Can the authors provide us with the mean axial length in the 3 groups, and the results of their comparison? The strategy used by the authors to compare the 3 groups was not appropriate. In Tables 2 and 3 before conducting intergroup comparisons (i.e., group A vs B, and group B vs C), the authors must first ensure that the 3 groups are statistically different, using a suitable global test such as an analysis of variance or a Kruskal– Wallis test. If the 3 groups are found to be statistically different with the global test, then the authors can proceed to the 3 pairwise comparisons; otherwise, the intergroup comparisons should not be conducted.4 Did the authors perform global tests before conducting intergroup comparisons and what was the degree of significance of these tests?
Furthermore, we have some concerns about the statistical analysis of their anatomic outcomes (i.e., the choroidal thickness at different locations of the posterior pole). Indeed, almost 10 different measures were compared and were simultaneously tested between each group in Tables 2 and 3, raising the major issue of multiple test adjustment and the likely correlation between all these measures.4 This makes the interpretation of the results in Tables 2 and 3 difficult, and conclusion should be reached with caution because of the increased risk of type I errors. For instance, concluding from the analysis (as the authors do) that the mean choroidal thickness, measured at 3 mm nasally (unadjusted P ⫽ 0.046), was different between idiopathic macular hole eyes and fellow eyes, is an overstatement of the statistical analysis presented in Table 2 and should be verified after multiple test adjustment. With this number of variables, it would be appropriate to adjust the P value (e.g., using the Bonferroni correction or the Holm procedure) before asserting any truly significant differences.4 Hence, we feel that the authors should verify their results after conducting multiple comparison adjustments. Finally, it seems that there is a misuse of the term of “choroidal perfusion” in the discussion that could be misleading for readers. The authors seem to use the terms of “choroidal thickness” and “choroidal perfusion” indifferently, whereas in their study they evaluated the choroidal thickness, and did not measure the choroidal perfusion. Indeed, one should keep in mind that choroidal thickness does not necessary reflect the choroidal perfusion. Interestingly, a very recent study has shown no correlation between the subfoveal choroidal thickness and the total choroidal blood flow and the subfoveal choroidal blood flow in healthy young subjects.5 We congratulate the authors on their informative article, and we hope these remarks will help them to improve the accuracy of their analysis and to confirm their interesting results.
MOHAMED EL SANHARAWI, MD, MPH1 OTMAN SANDALI, MD2 1
National Institute of Health and Medical Research, Cordeliers Research Center, Team 17, Physiopathology of Ocular Diseases, Therapeutic Innovations, Pierre and Marie Curie University, Paris, France; 2Department of Ophthalmology V, Quinze-Vingts National Ophthalmology Hospital, Paris, France The authors of the original article declined to reply.
References 1. Zeng J, Li J, Liu R, et al. Choroidal thickness in both eyes of patients with unilateral idiopathic macular hole. Ophthalmology 2012;119:2328 –33. 2. Reibaldi M, Boscia F, Avitabile T, et al. Enhanced depth imaging optical coherence tomography of the choroid in idiopathic macular hole: a cross-sectional prospective study. Am J Ophthalmol 2011;151:112–117.e2. 3. Li XQ, Larsen M, Munch IC. Subfoveal choroidal thickness in relation to sex and axial length in 93 Danish university students. Invest Ophthalmol Vis Sci 2011;52:8438 – 41. 4. Bender R, Lange S. Adjusting for multiple testing: when and how? J Clin Epidemiol 2001;54:343–9. 5. Sogawa K, Nagaoka T, Takahashi A, et al. Relationship between choroidal thickness and choroidal circulation in healthy young subjects. Am J Ophthalmol 2012;153:1129 –32.e1.