Evaluation of the orientation of the steepest meridian of regular astigmatism among highly myopic Egyptian patients seeking non-ablative surgical correction of the refractive error

INTRODUCTION: LASIK surgery is currently the preferred procedure to correct low to moderate myopia. The aim of this study was to determine the orientation of the steepest meridian of regular astigmatism in order to determine the relative incidence of vertical, horizontal, and oblique regular astigmatism among highly myopic Egyptian patients seeking non-ablative surgical correction of the refractive error. METHODS: One hundred and one eyes of 68 highly myopic patients who were seeking refractive surgery were included in this consecutive case series study. The refractive errors were measured using an autorefractometer and confirmed by trial. We measured the uncorrected and best corrected visual acuity in Snellen lines. Keratometry, central corneal thickness, and anterior chamber depth also were measured. The cylinder power in diopters and the axis in degrees were reported. Astigmatism was graded as with the rule (i.e., vertical meridian steeper), against the rule (i.e., horizontal meridian steeper), and oblique astigmatism. The number and the percentage of eyes with the rule, against the rule, and oblique astigmatism were calculated, and the chi-squared test was performed to analyze the data. RESULTS: The spherical refractive error ranged from −6.5 to −24.5 diopters (−13.45 ± 4.60). The cylinder power (Cyl) ranged from −0.25 to −7.5 diopters (−2.23 ± 1.28). The uncorrected visual acuity (UCVA) in Snellen lines ranged from 0.01 – 0.1 (0.03 ± 0.02). The mean for best corrected visual acuity (BCVA) in Snellen lines was 0.40 (± 0.23). The steepest meridian was vertical (i.e., with-the-rule astigmatism) in 44 eyes (43.56%), horizontal (i.e., against-the-rule astigmatism) in 27 eyes (26.73%), and oblique (i.e., oblique astigmatism) in 30 eyes (29.70%). CONCLUSIONS: The incidence of with-the-rule astigmatism in patients with high myopia was found to be much lower than in previous studies for non-myopic patients, with a higher incidence for against-the-rule astigmatism and oblique astigmatism.