Vector Analysis Of Keratorefractive Lenticule Excision For The Treatment Of Myopic Astigmatism

To analyse the efficacy of treatment of myopic astigmatism, one dioptre or greater, with keratorefractive lenticule excision (KLEx) using the using the Zeiss Visumax 500 (SMILE) and Visumax 800 (SMILEpro) femtosecond laser platforms.

A dedicated refractive surgical practice based in Christchurch, New Zealand.

A comprehensive database of all pre-operative, surgical and post-operative results for KLEx procedures has been maintained since implementation of KLEx in 2018. The analysis included 622 procedures for myopic astigmatism of one dioptre or more. Of these, 501 (80.5%) were SMILE procedures with the Zeiss Visumax 500 laser and 121 (19.5%) were SMILEpro procedures using the Visumax 800 laser. Both the Alpins method of vector analysis and the Journal of Cataract and Refractive Surgery (JCRS) double plot tool were utilized to assess accuracy if the astigmatic correction. Correction of with-the-rule, oblique and against-the-rule astigmatism were compared.  

The mean astigmatism correction was 1.60D ± 0.65D, with a range from 1.00 to 5.00D. There were 396 (63.7%) with-the-rule, 65 (10.5%) oblique and 161 (25.9%) against-the-rule astigmatism treatments. The average of the absolute value of angle of error was 6.6 degrees. The geometric mean of the correction index (ideally 1) was 0.88, indicating an under correction. The coefficient of adjustment geometric mean was 1.14. The geometric mean of the coefficient of adjustment for with-the-rule astigmatism was 1.19, for oblique astigmatism was 1.07 and for against-the-rule astigmatism was 1.05.

Vector analysis of SMILE and SMILEpro myopic astigmatism corrections shows an overall under correction of astigmatism. The under correction is greater for with-the-rule astigmatism, less for oblique astigmatism and least for against-the-rule astigmatism corrections.