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RESEARCH PRODUCT

Effect of cylinder power and axis changes on vision in astigmatic participants: A comment [letter]

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Dear editor We read with interest the article by Sha et al1 in the March 2019 issue. This study evaluated the effects of misalignment axis and undercorrecting cylinder powers on the visual performance of astigmatic people. The aim of this work was mainly to assist eye-care practitioners in reducing the number of toric contact lenses stock-keeping units. The authors analyze the effect of astigmatic undercorrection by 0.25, 0.50 and 0.75 DC, at different amounts of misalignments up to 30°. In this analysis, the effects of cylinder power, cylinder axis and their mutual interaction are analyzed separately. However, it is well known that cylinder power and axis are not independent variables; in fact, astigmatism is a vector magnitude. Several studies2, 4 use vector formalism to quantify the blur strength produced by astigmatism. Even in previous literature, 1 the authors show the power vector components (M, J0, J45) in Table 1, for the different groups in which the sample is divided. ...