Comment on: Refractive outcome analyses in myopes

Dear Editor, We read with great interest the recent article from Mitra et al. on refractive outcomes in myopes.[1] The main purpose of their work was to investigate the refractive accuracy of some of the currently available intraocular lens (IOL) calculation formulas for the prediction of the required lens power. We noted that they included only eyes implanted with the same IOL in the capsular bag. However, there is a number of points that we would like to point out. The size of the sample that was investigated in this study was limited (only 43 eyes), and testing for normality of the distribution should have been performed. We also raise criticism in relation to the large range of axial lengths included (24.75–32.35 mm): In this way, the authors included eyes with moderate, high and extreme myopia in the same sample. It is well-known that the IOL power prediction formula estimate the effective lens position in relation to the axial length and average corneal power, and notoriously perform worse in eyes with very long axial length. In addition, formulas might work unpredictably when abnormal corneal powers are involved, as in a fifth of the enrolled eyes. We would like to challenge the authors to agree that these limitations should be kept in mind by the readers, as might have potentially interfered with the study results. Perhaps the authors might provide the readership with graphs displaying the relation between absolute errors and axial length with the different formulas tested. Lastly, it was not clear why the authors used the mean numerical error as opposed to the mean absolute error for their analyses.