Excimer laser correction of astigmatism with multipass/multizone treatment

Purpose: To evaluate the accuracy of excimer laser correction of myopic astigmatism by multipass/multizone photoastigmatic refractive keratectomy (PARK). Setting: Tertiary referral ophthalmic hospital with an associated private laser facility. Methods: This study comprised a consecutive series of 332 eyes of 289 patients who were followed for 6 months. All patients were 18 years or older, had stable myopic astigmatism (up to a -19.0 diopters [D] spherical equivalent [SE] at the spectacle plane), and had a best corrected visual acuity of at least 20/60 in both eyes. All eyes were treated with a VISX Twenty-Twenty excimer laser. The correction was divided between ablation zones using a multipass/multizone treatment paradigm based on the amount of myopia and astigmatism. Patients were examined 1 week, and 1, 3, and 6 months after surgery. Results: Analysis of the mean percentage of spherical correction across the range of myopic preoperative SEs treated demonstrated 90% correction for most amounts of myopic astigmatism. Eyes with low myopia (mean preoperative SE ≤-5.0 D) treated with ≤-1.0 diopter cylinder (DC) of astigmatism achieved a mean percentage of spherical correction of 91% versus 93% in eyes with high myopia (>-5.0 D mean preoperative SE). Eyes with low myopia treated with >-1.0 DC of astigmatism achieved a mean percentage spherical correction of 90% versus 89% in eyes with high myopia. The differences between the two groups were not statistically significant. Patients with high relative cylinder (>80% of total sphere treated) achieved comparable results. Analysis of the astigmatic component of the treatment, independent of the spherical result, showed a trend toward overcorrection in the high myopia group with less than -1.0 DC and a mean astigmatic correction of 89 and 98%, respectively, in the low and high myopic astigmatism groups. The mean angle of error was +2.0 degrees. Conclusion: Multipass/multizone PARK for myopic astigmatism demonstrated a high degree of predictability and stability with desirable results for low and high levels of astigmatism across the range of myopic astigmatism treated by surface ablation.