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M.V. Subbaram, S.M. MacRae, G. Yoon; Causes of Postoperative Astigmatism With Myopic Custom Ablation . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3610.
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© ARVO (1962-2015); The Authors (2016-present)
To determine the prognostic factors for postoperative astigmatism following custom LASIK for myopia correction.
Retrospective data analysis was performed on 175 eyes (89 patients, mean SE: –4.89±2.06 D, mean cylinder: –0.82±0.71 D, mean HORMS: 0.53±0.16 µm @6mm aperture) treated using Zyoptix platform. Discrepancy in preoperative wavefront and manifest subjective refractions were compared between eyes that developed postoperative astigmatism ≥ 0.50D and those with postoperative astigmatism < 0.50D. Optical convolution was performed separately to investigate any optical relation between higher order aberrations and astigmatism.
71 eyes (40.6%) developed postoperative manifest astigmatism ≥0.50D. Greater preoperative coma (0.40±0.17µm) was measured among eyes that developed postoperative astigmatism ≥0.50D than among eyes without postoperative astigmatism (< 0.50D; mean: 0.26±0.43 µm; p < 0.001). Rotation in postoperative manifest astigmatism axis, relative to preoperative astigmatism axis, was 49.21±26.87° when preoperative wavefront astigmatism > preoperative subjective manifest astigmatism (astigmatic overcorrection). This axis rotation was significantly greater than an axis rotation of 28.28±20.70° when preoperative wavefront astigmatism < preoperative subjective manifest astigmatism (astigmatic undercorrection; p<0.001).
Optical convolution revealed a significant optical relationship between 2nd order astigmatism and 4th order secondary astigmatism (3:1 ratio). 3rd order coma could induce 2nd order astigmatism with decentration from pupil center shift with dilation and/or ablation zone decentration.
Preoperative coma and discrepancy in preoperative astigmatism values between wavefront and manifest subjective cylinder refractions are risk factors for inducing postoperative astigmatism following custom LASIK.
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