Sir,
We thank Dr Garcia Medina for his interest in our article. In his study,1 Dr Garcia Medina and his team conducted a study using the same instrument, namely GDx Access with variable corneal compensation (VCC). Dr Garcia Medina enquired whether we used VCC in our study. The answer is yes. All measurements were taken using GDx Access using default setting, that is, with VCC enabled. As we did not modify the machine setting, we thought that specifying this in the text would have been redundant. However, we thank Dr Garcia Medina for giving us the possibility of clarifying this detail.
As far as the discordance between our results and his, we respectfully remind Dr Garcia Medina that no more than 28 eyes were included in his larger study. When we set up our study, we determined that the minimum sample size to have a statistical power of 80% with an alpha error of 0.05 and an effect size of medium magnitude (d=0.5) would have been 102 eyes. We would like to highlight how all these parameters are considered to be the norm in sample size calculations. Given the sample size reported by Dr Garcia Medina, the power of his study results to be less than 40%. While his methodology is faultless, perhaps his group might want to consider repeating the study with a larger sample in order to achieve a more robust analysis.
References
Garcia Medina JJ, Garcia Medina M, Dorta SG . Effect of posterior capsular opacification removal on scanning laser polarimetry measurements. Graefe Arch Clin Exp Ophthalmol 2006 March 22, doi:10.1007/s00417-005-0244-8.
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Vetrugno, M., Masselli, F., Greco, G. et al. Reply to Dr Gracia–Medina. Eye 21, 265 (2007). https://doi.org/10.1038/sj.eye.6702506
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DOI: https://doi.org/10.1038/sj.eye.6702506