Efficacy of Cylindrical Correction in Wavefront-guided Advanced Surface Ablation with Iris Registration for Myopic Astigmatism

Abstract

Purpose: : To assess the efficacy of cylindrical correction in Wavefront-guided Advanced Surface Ablation (WF-ASA) with iris registration (IR) in patients with myopic astigmatism.

Methods: : 240 eyes with myopia, astigmatism and wavefront (WF) aberrations undergoing WF-ASA with IR (STAR S4 IR^TM, AMO) were retrospectively analyzed. WF (WaveScan WaveFront^TM, AMO) and manifest refractions were obtained 1 week before and 3 months after WF-ASA. Reduction in astigmatic amplitude (RAA = Postop cyl - Preop cyl) and degree of achieved cylindrical correction (ACC = amplitude and angle) by vector analysis was used to assess efficacy of treatment.

Results: : Preoperative mean spherical refraction by WF and manifest was alike -4.35D ±2.0D (-0.25 to -8.5D) but WF mean astigmatism 0.70±0.50 D (0.06 to 2.49D) was significantly higher than manifest (0.56±0.53 D) P<0.05. At 3 months, mean RAA by WF refraction (0.33±0.44D) was significantly lower than mean RAA by manifest refraction (0.45±0.58D) P=0.001. However, ACC by vector analysis showed comparable amplitudes for WF (0.52±0.43) and manifest (0.54±0.54D) refractions. Treatment axis and astigmatic axis differed significantly (P<0.01) with alignment errors showing significant difference between WF (13.0±12.1°) and manifest (2.2±7.4°) refraction (P<0.001).There was no correlation between alignment error and mean preop cylinder. At least 0.25D increase in astigmatism was observed in a small group (WF=13, manifest=18 eyes of which 7 and 10 eyes respectively had an increase of ≥0.50D). Astigmatism of ≥0.25D was induced in 10 of the 15 eyes without any manifest preop astigmatism.

Conclusions: : Overall, WF-ASA with IR is an effective and safe treatment for myopic astigmatism. In our study, ACC matches the intended correction closely (<0.2D difference on average), however significant alignment error reduced the efficacy of the reduction in astigmatism.

Keywords: clinical (human) or epidemiologic studies: outcomes/complications • refractive surgery: PRK • astigmatism