Laser in Situ Keratomileusis for the Correction of Myopia and Myopic Astigmatism

Purpose: To evaluate the efficacy, safety, predictability, and surgically induced astigmatism (SIA) of laser in situ keratomileusis (LASIK) for the correction of myopia and myopic astigmatism. Setting: Department of Ophthalmology, National Taiwan University Hospital, Taipei, Taiwan. Methods : This retrospective study comprised 69 eyes that had LASIK to correct myopia and 74 eyes that had LASIK to correct myopic astigmatism. The excimer laser keratectomy was performed using a Summit Apex Plus((R)) machine. Refraction, visual acuity, and computerized corneal videokeratography data from the preoperative and postoperative examinations were collected, The astigmatic change was calculated by the Alpins vector analysis method. Results: The preoperative spherical equivalent at the glasses plane in the myopia and myopic astigmatism groups was -8.08 diopters (D) and -9.73 D , respectively. At 6 months, the spherical equivalent and residual corneal astigmatism were -0.25 D and 0. 85 D, respectively, in the myopia group and -0.71 D and 0.82 D, respectively, in the myopic astigmatism group. In the myopia group, 88% of eyes were within +/- 1.0 D of the intended myopia correction and in the myopic astigmatism group, 85% were within +/- 1.0 D of the targeted spherical equivalent and 90% were within +/- 1.0 D of the intended astigmatism correction. The uncorrected visual acuity was 20/40 or better in 94.1% of eyes in the myopia group and 92.5% of eyes in the myopic astigmatism group. The SIA magnitude was 0.66 D with the axis randomly distributed in the myopia group. The mean astigmatism correction index was 0.97, the mean magnitude of error was 0.13 D +/- 0.62 (SD), and the mean angle of error was -3.70 +/- 13.73 degrees in the myopic astigmatism group . Conclusion: Laser in situ keratomileusis had similar predictability, safety, and efficacy in the treatment of myopia and myopic astigmatism, The astigmatism correction was effective, but the results suggest that subjective astigmatism of less than 1.0 D need not be treated with the Summit Apex Plus laser. (C) 2001 ASCRS and ESCRS