Reply: We thank Wallerstein and Gauvin for their insightful comments related to our recent publication.1 We also appreciate their important work in this field.
Suggesting a trend to better postoperative SEQ, as they do, is one of the means by which readers can become confused. Having set a criterion for statistical significance, the study results determine whether differences can be stated as such. Our reported P value of .25 does not approach the .05 cutoff we established for a statistically significant difference and would not suggest a trend to most statisticians. Furthermore, we have indicated in the article that refractions were not always consistent with visual acuity findings. This is a recognized limitation of retrospective data collection.
As was also noted, the astigmatic analysis suggested was not conducted. This was not because of lack of astigmatism data but because of the recognized variability in those data. We did not feel the results would be meaningful based on the variability in refractions that we noted in our results.
Wallerstein and Gauvin also noted that the differences in nomograms would impact outcomes. However, site-specific nomograms are not unusual. As outlined in the Methods section of our study, nomogram adjustments were permitted in both groups of data, so the outcomes from both manifest and Phorcides planning would be affected. There is no reason to suspect a specific nomogram bias in the manifest group.
One of the strengths of our study (which was considered a weakness by Wallerstein and Gauvin in their commentary) was that comparative data were collected from 4 different sites, using different nomograms, and included both manifest and Phorcides data. Refractions were slightly more variable, and visual acuity data were collected less stringently than might be the case for a prospective trial. However, there is no reason to believe that there would be a difference between the data collection based on whether the eye was treated on the manifest refraction or based on Phorcides data. This is particularly the case with comanaged data. What is perhaps most important in our analysis is that, despite these limitations, significant relative differences in the results were evident.
The comparison provided related to the results for 3449 eyes matched to the inclusion/exclusion criteria of the current study does not provide any indication that the eyes were matched in any other way. Refractive error, topography, and differences between corneal and refractive astigmatism are all likely to be different in these datasets. The comparisons, thus, cannot be presumed to be based on matched data, and as such, they are not particularly meaningful. Furthermore, results reported for these 3449 eyes seem significantly better than anything previously published by the authors of this letter.2,3
We must note that the degree of precision adopted by Wallerstein et al. in their clinic is to be admired. We know of few sites that will average up to 3 manifest refractions (although the way in which these are averaged is unspecified) per eye and analyze between 4 and 8 corneal topographies to determine the best treatment parameters.2 The results they achieve are correspondingly good. We can only imagine what results such an approach, augmented by the Phorcides Analytical Engine, might produce. We would encourage them to perform such a comparative trial.
Finally, as noted in our comments regarding the limitations of the current study, a prospective trial of the Phorcides Analytical Engine would be helpful in corroborating the findings here. We have initiated such a trial and hope to report the results in future.
—Mark Lobanoff, MD, Karl Stonecipher, MD, Richard Potvin, OD.
1. Lobanoff M, Stonecipher K, Tooma T, Wexler S, Potvin R. Clinical outcomes after topography-guided LASIK: comparing results based on a new topography analysis algorithm with those based on manifest refraction. J Cataract Refract Surg 2020;46:814–819
2. Wallerstein A, Gauvin M, Qi SR, Bashour M, Cohen M. Primary topography-guided LASIK: treating manifest refractive astigmatism versus topography-measured anterior corneal astigmatism. J Refract Surg 2019;35:15–23
3. Wallerstein A, Gauvin M, Qi SR, Cohen M. Effect of the vectorial difference between manifest refractive astigmatism and anterior corneal astigmatism on topography-guided LASIK outcomes. J Refract Surg 2020;36:449–458