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Reply to comment on: Rethinking the optimal methods for vector analysis of astigmatism

Koch, Douglas D. MD; Wang, Li MD, PhD; Holladay, Jack T. MD; Abulafia, Adi MD; Hill, Warren MD

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Journal of Cataract & Refractive Surgery: January 2021 - Volume 47 - Issue 1 - p 139
doi: 10.1097/j.jcrs.0000000000000522
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We appreciate Dr. Alpins' comments and are pleased to respond. We do want to acknowledge how accessible and easy to use his system is. That is a goal to which all complex methods of analysis should aspire, and it is what we tried to accomplish with the Astigmatism Double-Angle Plot, Corneal SIA, and IOL Calculation Formula Analyzer tools developed by Dr. Abulafia and now available on the ASCRS, ESCRS, and JCRS websites.

Our premise is that the complicated topic of astigmatism analysis requires methods of analysis that accurately convey the results and the deviations from the intended target. We hold to our concerns about some of the ASSORT® displays, specifically:

  1. The Assort double-angle plots are double-angle plots that, instead of using the correct 180-degree labeling, are mislabeled with 360-degree labeling, which will cause the reader to misinterpret the results and certainly will not help readers understand the concept of doubling the angles.
  2. Univariate plots of vector magnitudes and angles that are not helpful because one cannot link magnitude errors to the angles of these vectors. Dr. Alpins said, of the outlier values that we illustrated: “Such cases would always need to be examined comprehensively to determine the underlying cause.” But that is precisely our point: Without knowing both magnitude and angle of any given data point, one cannot know which data need to be examined further.
  3. The correction index that is confusing and could lead to adjustments in treatment parameters that will worsen outcomes. Our 2 cases demonstrate this. Dr. Alpins states of the correction index, “A quick glance then allows the surgeon to see whether there are differences in effect between with-the-rule, against-the-rule, and oblique treatments.” That is certainly not true of our cases. For example, the case with the oblique error has the correction index plotted along 180 degrees, when the error is in fact at 148 degrees. The correction index angle for this sample case is simply incorrect.

Authors who choose to use these particular ASSORT displays do so at the risk for not truly characterizing or even misconstruing what occurred. Journal standards need to be accurate and informative. We recognize that there is room for further development of optimal means of displaying and statistically analyzing astigmatic outcomes and look forward to continuing this exploration with the many colleagues who have contributed so much.

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