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Timothy J Archer, Dan Z Reinstein, Glenn Ian Carp, Marine Gobbe; Accuracy of Astigmatism Correction with SMILE. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):3926.
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© ARVO (1962-2015); The Authors (2016-present)
To report the accuracy of refractive astigmatism correction using small incision lenticule extraction (SMILE).
This was a retrospective analysis of 313 consecutive eyes with myopic astigmatism treated by SMILE using the VisuMax femtosecond laser (Carl Zeiss Meditec). Inclusion criteria were spherical equivalent (SEQ) treated up to -10.00 D, refractive astigmatism treated of 0.75 D or more, and 3 month follow-up data available. A personalized nomogram was used for all treatments. Vector analysis was performed to evaluate the accuracy of the refractive astigmatism correction using the Alpins method. The analysis was then repeated for groups according to the axis of astigmatism (positive cylinder notation): with-the-rule (WTR, 60˚ to 120˚), oblique (30˚ to 60˚ and 120˚ to 150˚), and against-the-rule (ATR, 0˚ to 30˚ and 150˚ to 180˚).
Mean SEQ treated was -4.84±2.01 D (range: -0.75 to -10.00 D). Mean refractive astigmatism treated was 1.29±0.62 D (range: 0.75 to 4.25 D). Including all eyes, the arithmetic mean of the Difference Vector was 0.37 D (indicating this magnitude of refractive astigmatism remaining postoperatively). The vector mean of the Difference Vector was 0.12 D Ax 18. The geometric mean of the Correction Index (CI) was 1.08 (indicating a slight overcorrection), but the fan graph showed that the CI was >1 (overcorrected) for the majority of eyes with ATR astigmatism. The slope of the scatter plot of Target Induced Astigmatism (TIA) vs Surgically Induced Astigmatism (SIA) was 1.09 (indicating a slight overcorrection), compared to 0.86 when using the laser data entry as the TIA. The arithmetic mean of the Angle of Error was 0.28±8.19˚ and this was greater than 15˚ in only 6% of eyes (indicating no systematic rotational/cyclotorsion error). The slope of the TIA vs SIA scatter plot was 1.07 for the WTR group (n=175), 1.15 for the oblique group (n=48), and 1.32 for the ATR group (n=90) - indicating a greater overcorrection moving from WTR to ATR astigmatism
Use of a personalized nomogram improved the accuracy of SMILE astigmatism correction. This may be further improved by using a continuous function according to the axis of the astigmatism.
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