Re: Turnbull et al.: Methods for intraocular lens power calculation in cataract surgery after radial keratotomy (Ophthalmology. 2020;127:45-51)

Abstract

TO THE EDITOR: We read with interest the article by Turnbull et al 1 concerning intraocular lens (IOL) power calculation after radial keratotomy. We would like to congratulate the authors for their article because this is an important topic. However, we would like to make some comments on points that, in our opinion, should be clarified. First, the authors stated that they did not perform the zeroing of the mean error because of the high heterogeneity of unusual subsets, such as post-radial keratotomy eyes. Moreover, they assert that it is considered inappropriate to derive optimized IOL constants in clinical practice because they are unlikely to be accurate or applicable to future cases. We agree with this last consideration; however, the methodology of zeroing out the mean error currently is not adopted in clinical practice, but only to compare the results in experimental evaluation of IOL power accuracy, according to protocols of Hoffer et al. 2 Second, we also have some concerns about the Wilcoxon signed-rank test used by the authors to compare the absolute errors obtained by different methods because rank tests could have a low power and could be affected by outliers. It would be preferable to use bootstrapped estimates when performing t tests and confidence intervals after zeroing out the mean error. 3 Third, we would also comment on the number of evaluated eyes, 52 eyes of 34 patients, meaning that only in some patients both eyes were studied. We agree with authors that this choice allows to avoid "wastage" of valuable data, but when analyzing datasets that include some subjects with 1 eye and others with 2 eyes, it should be advisable to apply specific statistical methods such as the Bootstrap or generalized estimating equations to have valid results. 2 Fourth, several reports in the literature described formulas to calculate IOL power mainly after photorefractive keratectomy and LASIK, but only few after radial keratotomy. 4 The authors checked some of them, but not evaluated others such as the contact lens method described by Soper et al 4 and the method based on a regression formula applied to R Factor method, proposed by Rosa et al. 5 We understand why the authors could not compare the method by Soper et al, but the formula described by Rosa et al did not require the knowledge of patient's history, neither special examination, and this method has demonstrated to improve refractive outcomes and we wonder why it was not evaluated among the other no-history methods.

The impact of corneal higher-order aberrations on dynamic visual acuity post cataract surgery

“…Fifth, the present research includes some subjects with both eyes. The inter-eye correlation could affect the statistical significance when bilateral eyes are included in the same group ( Hoffer et al, 2015 ; De Bernardo et al, 2020 ). Random choice of eyes in a single subject should be adopted in future studies.…”

Recent Evidence of Tea Tree Oil Effectiveness in Blepharitis Treatment

“…To be able to cure blepharitis before anterior segment ocular surgery, such as cataract extraction [8,9] or refractive surgery [10][11][12][13], could be very important [14,15], primarily to lower the chance of endophthalmitis.…”

Comment on: Efficacy of segmented axial length and artificial intelligence approaches to intraocular lens power calculation in short eyes

“…We applaud the adoption of the generalized estimating equation to account correlations between both eyes of the same patient, which is mandatory in this scenario. 4 On the other hand, we wonder why the authors chose the mean absolute error (MAE) instead of the median absolute error (MedAE). The MedAE is less affected by outliers than the MAE, and the distribution of the absolute PE is not Gaussian, as reported by the same authors, and it is described better by the MedAE than by the MAE.…”