Assessment of the effects of LASIK on astigmatism of-2.0D or above by corneal topography

Abstract

Objective To investigate the accuracy of the effects of laser in situ keratomileusis (LASIK) on astigmatism of -2.0D or above assessed by corneal topography.Methods Thirty-six eyes of 25 patients with astigmatism of-2.0D or above who underwent LASIK were included in this retrospective study. Corneal topography and subjective refraction examination were performed before and at least 6 months after surgery.The astigmatism of subjective refraction was translated to cylinder diopter of corneal plane.Astigmatism measured with corneal topography and that of subjective refraction was compared before and after the surgery. Results The mean astigmatism measured by corneal topography was (-2.29±0.61) D and (-1.91±0.68) D pre- and postoperative respectively.The meaa astigmatism in corneal plane measured by manifest refraction was (-2.22±0.61) D and (-0.46±0.43) D pro- and postoperative respectively.The differences between pre- and post-operation were both statistically significant (P<0.05).The mean difference between pre- and post-operation in axis of astigmatism measured by corneal topography and manifest refraction was 3.19±3.04 degree and 29.61±29.49 degree, respectively.The meaa difference in axis of astigmatism measured by corneal topography and manifest refraction was (6.53±14.19) degree preoperatively.The difference in magnitude of refractive and corneal astigmatism was not statistically significant preoperatively (P =0.54), but was significant postoperatively (P=0.00).Conclusions Astigmatism of-2.0D or above measured by corneal topography has agreement with that measured by subjective refraction pre-operatively, however, the astigmatism post-LASIK can always be overestimated by corneal topography. Key words: Astigmatism; Corneal topography; Laser in situ keratomileusis