We read with interest the paper by Zhu and associates, who investigated the relationship between the postoperative refractive error and fixation stability in highly myopic eyes that had cataract surgery. They found that hyperopic errors were correlated to reduced fixation ability and came to the conclusion that fixation stability may play a causative role in the postoperative refractive error. This hypothesis is intriguing, but their results are biased by at least 2 issues. First, the refractive error was calculated as the difference between the measured postoperative refraction and the targeted refraction. This approach is not correct, since what we need to know is the prediction error (PE), that is, the difference between the postoperative refraction and the refraction predicted by the formula (not the surgeon’s target). This has been clearly explained in our editorial. Second, it seems that constant optimization was not performed in order to zero the mean arithmetic PE before making comparisons. Constant optimization in highly myopic eyes can lead to unusual values and should be carried out separately in eyes with positive and negative intraocular lenses. Using optimized constants reduces the risk of hyperopic outcomes and may easily influence the correlation with fixation stability.
Hence we would be grateful if the authors could repeat their analysis following the above-mentioned procedures and thus confirm their results as legitimate.