Correction of myopic astigmatism with the VISX 20/20 excimer laser. An overview of treatment outcome

Abstract

The advent of the excimer laser has brought about the potential for improved vision in many individuals with myopia and astigmatism. However, photoastigmatic refractive keratectomy (PARK) remains a matter of controversy. The purpose of our study was to determine the predictability of VISX 20/20 excimer laser photorefractive keratectomy in the treatment of myopic astigmatism. Our study comprised 31 eyes of 22 patients with myopic astigmatism. All patients underwent treatment with a VISX 20/20 excimer laser and were followed up for 6 months. Complete 12-month follow-up data were available from 18 eyes. Park was performed in eyes with myopia between -1.5 and -10.0 D and with astigmatism between -0.5 and -5.5 D. Thus, the corresponding spherical equivalent ranged from -1.75 to -10.5 D. Six months postoperatively, 21/31 (62%) eyes were within +/- 1.0 D of the target refraction and 13/31 (42%) within +/- 0.5 D of the target refraction. In 13 of 15 eyes (87%) with myopia less than -6.0 D, an uncorrected visual acuity of at least 0.8 was noted. In eyes with myopia greater than -6.0 D, 9/16 (56%) showed an uncorrected visual acuity of at least 0.5. Six months after PARK, an increase of one line on the Snellen Visual Acuity Chart was observed in 8/31 (26%) and an increase of two lines was noted in eyes 3/31 (10%). One of 31 eyes (3%) showed an increase of three lines. A decrease in visual acuity of 1 line on the Snellen Visual Acuity Chart was found in 4/31 (13%), and in 3/31 eyes (10%) a decrease of 2-4 lines was noted. Overall, we observed a statistically significant reduction of astigmatism from 1.93 +/- 1.43 D to 0.93 +/- 0.63 D. Reduction of corneal astigmatism less than -1.25 D was not statistically significant. In eyes with astigmatism ranging from -1.25 to -2.5 D or greater than -2.75 D, a significant reduction of the mean astigmatism was noted. The postoperative regression of astigmatic correction was low. However, an axis shift of more than 15 degrees was found in 42%/35% of eyes by subjective refraction (miosis/cycloplegia) and in 33% in corneal topography. No central islands were noted. Photoastigmatic refractive keratectomy (PARK) constitutes a potential means of correcting myopic astigmatism. In eyes with astigmatism greater than -1.0 D a significant reduction of 60% of the mean astigmatism was noted. However, the considerable proportion of eyes with a postoperative axis shift greater than 15 degrees and a decrease in visual acuity of two or more lines indicates that further research is needed on excimer laser surgery to improve the reliability and safety.