Evaluation of axis alignment system for correction of myopic astigmatism with the excimer laser

Purpose: To evaluate the efficacy of in situ axis alignment for the treatment of myopic astigmatism with an excimer laser. Methods: In this prospective clinical trial, 71 eyes with stable astigmatism of -1.00 to - 6.00 diopters (D) with or without stable myopia of up to 10.00 D were randomized to receive excimer treatment of their astigmatic component aligned to the axis determined by subjective refraction (control group) or to have the alignment verified and altered if necessary by in situ alignment (axis alignment group). A VISX Twenty-Twenty excimer laser was used for the treatment. Patients were followed for 6 months. Results: In 85% of eyes in the axis alignment group, the axis of cylinder was different from that calculated by routine refraction. Pretreatment mean cylinder was -1.81 D ± 0.91 (SD) in the axis alignment group and -1.75 ± 0.60 D in the control group. At 6 months, an undercorrection of cylinder was seen in both groups; the mean residual cylinder was -0.70 ± 0.56 D in the axis alignment group and -0.59 ± 0.50 D in the control group. More than 80% of all eyes were within ±1.00 D of plano and achieved an uncorrected visual acuity of 6/12 or better. A loss of two or more lines of best corrected visual acuity was recorded in three eyes. Conclusion: The in situ alignment technique did not produce better results of photoastigmatic refractive keratectomy than the routine axis alignment technique.