EXCIMER-LASER CORRECTION OF ASTIGMATISM WITH MULTIPASS MULTIZONE TREATMENT/

Purpose: To evaluate the accuracy of excimer laser correction of myopi c astigmatism by multipass/multizone photoastigmatic refractive kerate ctomy (PARK). Setting: Tertiary referral ophthalmic hospital with ari associated private laser facility. Methods: This study comprised a con secutive series of 332 eyes of 289 patients who were followed for 6 mo nths. Ail patients were 18 years or older, had stable myopic astigmati sm (up to a -19.0 diopters [D] spherical equivalent [SE] at the specta cle plane), and had a best corrected visual acuity of at least 20/60 i n both eyes. All eyes were treated with a VISX Twenty-Twenty excimer l aser. The correction was divided between ablation zones using a multip ass/multizone treatment paradigm based on the amount of myopia and ast igmatism) Patients were examined 1 week, and 1, 3, and 6 months after surgery. Results: Analysis oi the mean percentage oi spherical correct ion across the range of myopic preoperative SEs treated demonstrated 9 0% correction for most amounts of myopic astigmatism Eyes with low myo pia (mean preoperative SE less than or equal to-5.0 D) treated with le ss than or equal to-1.0 diopter cylinder (DC) of astigmatism achieved a mean percentage of spherical correction of 91% versus 93% in eyes wi th high myopia (>-5.0 D mean preoperative SE). Eyes with low myopia tr eated with >-1.0 DC of :astigmatism achieved a mean percentage spheric al correction of: 90% versus 89% in eyes with high myopia. The differe nces between the two groups were not statistically significant. Patien ts with high relative cylinder (>80% of total sphere treated) achieved comparable results. Analysis of the astigmatic component of the treat ment, independent of the spherical result, showed a trend toward overc orrection in the high myopia group with less than -1.0 DC and a mean a stigmatic correction of 89 and 98%, respectively, in the low and high myopic astigmatism grp:ups. The mean angle of error was +2.0 degrees. Conclusion: Multipass/multizone PARK for myopic astigmatism demonstrat ed a high ;degree of predictability and stability with desirable resul ts for low and high levels of astigmatism across the range of myopic a stigmatism treated by surface ablation.