Comment on: Intraocular lens power calculation with ray tracing based on AS-OCT and adjusted axial length after myopic excimer laser surgery : Journal of Cataract & Refractive Surgery

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Comment on: Intraocular lens power calculation with ray tracing based on AS-OCT and adjusted axial length after myopic excimer laser surgery

Cione, Ferdinando MD; De Bernardo, Maddalena MD, PhD; Rosa, Nicola MD

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Journal of Cataract & Refractive Surgery: November 2022 - Volume 48 - Issue 11 - p 1349
doi: 10.1097/j.jcrs.0000000000001057
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We read the article by Savini et al. concerning ray-tracing–based intraocular lens (IOL) power calculation after myopic laser refractive surgery (LRS).1 Two of these authors (S.G., H.J.K.) proposed the most up-to-date guidelines in this field,2 and we were surprised by some critical issues of this paper that must be clarified.

The authors evaluated postoperative refraction at 4 m. S.G. and H.J.K. in a previous paper recommended to use 6 m testing distance to evaluate refractions, and if 4 m is used, the value of −0.08 diopter should be added to the spherical equivalent, but this correction was not reported.2

A sample size of 32 eyes was calculated according to a study published by Wang et al. in 2019.3 We were surprised because S.G. and H.J.K., in a more recent study published in 2021, suggested to evaluate at least 50 eyes with previous LRS.2 Moreover, in the same study, they stated that a detailed sample size calculation should be preferred and the effect size, that they did not specify, is required.2

Different types of IOLs can be acceptable, but 2 toric IOLs have been included in this study.4 We wonder if even this is correct.

The authors stated that constant optimization through zeroing out the mean prediction error was not performed because the sample was made up of long eyes.1 This seems to contradict a previously published paper by S.G. and H.J.K. that reported constant optimization to be preferable when analyzing post-LRS eyes, that usually are long eyes.2 In addition, in this study, only some mean prediction errors were not significantly different from zero, meaning that a systematic error persists in others, making, according to these authors, constant optimization essential.

However, what really astonished us is that the authors declared that they analyzed 39 eyes of 39 patients, implying that only 1 eye for each patient was evaluated.1 Unfortunately, this is not true, as shown in the Supplementary Material section, where it is possible to look up the database of the study (available at, accessed on August 3, 2022). Ignoring the indefensible absence of anonymization, it is evident that both eyes were analyzed in at least 9 patients. Therefore, only 30 patients or less were evaluated. According to what S.G. and H.J.K. stated in a previous paper, measurements from fellow eyes cannot be treated as if they were independent.2 Ignoring intereye correlation can lead to smaller P values when both eyes are in the same group.5 We wonder why the authors reported misleading information in their manuscript: specific statistical methods such as the bootstrap or generalized estimating equations could have been performed to consider intereye correlation and have valid results.2

In conclusion, according to the abovementioned protocols, the results of this study should be considered unreliable.2 In the light of the misleading information, it is a shame that such a paper has been accepted by the reviewers for publication in such a prestigious journal, but we wonder if we can trust the previously published papers by the same authors.


1. Savini G, Hoffer KJ, Ribeiro FJ, Dias JM, Coutinho CP, Barboni P, Schiano-Lomoriello D. Intraocular lens power calculation with ray tracing based on AS-OCT and adjusted axial length after myopic excimer laser surgery. J Cataract Refract Surg 2022;48:947–953
2. Hoffer KJ, Savini G. Update on intraocular lens power calculation study protocols: the better way to design and report clinical trials. Ophthalmology 2021;128:e115–e120
3. Wang L, Spektor T, de Souza RG, Koch DD. Evaluation of total keratometry and its accuracy for intraocular lens power calculation in eyes after corneal refractive surgery. J Cataract Refract Surg 2019;45:1416–1421
4. Rosa N, Cione F, Pepe A, Musto S, De Bernardo M. An advanced lens measurement approach (ALMA) in post refractive surgery IOL power calculation with unknown preoperative parameters. PLoS One 2020;15:e0237990
5. Ying GS, Maguire MG, Glynn R, Rosner B. Tutorial on biostatistics: statistical analysis for correlated binary eye data. Ophthalmic Epidemiol 2018;25:1–2

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