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Abstract

We appreciate De Bernardo and coworkers’ interest in this topic and their comments on our article. We elected not to optimize intraocular lens constants and zero the mean error in this series because improving outcomes by using atypical constants is of little practical benefit in atypical eyes. We fully agree that zeroing the mean error should be done when comparing formula performance in series of normal eyes, and this is what we have done in our previous publications. What is required in unusual subsets is a formula that can be used with the same constants as normal eyes and still provide accurate outcomes. Regarding the statistical comparison of absolute errors that lack a normal distribution, the Wilcoxon test is commonly recommended for this purpose.1Wang L. Koch D.D. Hill W. et al.Pursuing perfection in intraocular lens calculations: III. Criteria for analysing outcomes.J Cataract Refract Surg. 2017; 43: 999-1002Abstract Full Text Full Text PDF PubMed Scopus (95) Google Scholar Other statistical methods could be used, but it is unlikely that they would change the material findings of our study. Generalized estimating equations have a role when adjusting for the use of bilateral eyes that tend to have a similar outcome, but their use tends to be reserved for larger studies. Using this method to compensate for relatively low numbers of atypical cases was not considered appropriate because it was likely to result in an underestimation of significance and loss of valuable data. Our study was designed to compare the True K formula with other intraocular lens calculation methods commonly used to deal with eyes after radial keratotomy (predominantly those included in the American Society of Cataract and Refractive Surgery calculator), rather than serve as an exhaustive review of all methods. The R Factor method was initially described by Rosa et al2Rosa N. Capasso L. Lanza M. et al.Reliability of a new correcting factor in calculating intraocular lens power after refractive corneal surgery.J Cataract Refract Surg. 2005; 31: 1020-1024Abstract Full Text Full Text PDF PubMed Scopus (40) Google Scholar in 2005 for use after LASIK and photorefractive keratectomy, but so far has not gained traction in terms of being included in either the American Society of Cataract and Refractive Surgery calculator or other recent reviews of this topic.3Ma J.X. Tang M. Wang L. et al.Comparison of newer IOL power calculation methods for eyes with previous radial keratotomy.Invest Ophthalmol Vis Sci. 2016; 57: OCT162-168Crossref PubMed Scopus (23) Google Scholar,4Savini G. Hoffer K.J. Intraocular lens power calculation in eyes with previous corneal refractive surgery.Eye Vis. 2018; 5: 18Crossref PubMed Scopus (49) Google Scholar In a 2011 study of 9 intraocular lens calculation formulae for postmyopic LASIK eyes, several of which have since been superseded by improved methods, the R Factor was found to be one of the least accurate.5McCarthy M. Gavanski G.M. Paton K.E. et al.Intraocular lens power calculations after myopic laser refractive surgery: a comparison of methods in 173 eyes.Ophthalmology. 2011; 118: 940-944Abstract Full Text Full Text PDF PubMed Scopus (98) Google Scholar We admit to not being aware of the R Factor being used in the context of post-radial keratotomy eyes, which differ considerably from post-LASIK and photorefractive keratectomy eyes, and indeed a Pubmed search of [“radial keratotomy” AND “R factor”] performed on April 29, 2020 returned zero results. Re: Turnbull et al.: Methods for intraocular lens power calculation in cataract surgery after radial keratotomy (Ophthalmology. 2020;127:45-51)OphthalmologyVol. 127Issue 10PreviewWe read with interest the article by Turnbull et al1 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. Full-Text PDF