Photorefractive keratectomy to correct myopic or hyperopic astigmatism with a cross-cylinder ablation

PURPOSE: To assess the efficacy and safety of a combined ablation of the st eep and flat meridian to correct astigmatism with the excimer laser. METHODS: Twenty-two eyes with myopic, mixed, or hyperopic astigmatism (mean preoperative spherical equivalent refraction -4.30 +/- 4.70 D [range, -12. 50 to +1.50 D] and mean preoperative cylinder magnitude -3.40 +/- 1.40 D [r ange, -1.50 to -6.00 D]) underwent PRK with the Nidek EC-5000 excimer laser . The surgical strategy involved ablating half the amount of the cylinder t in diopters) along steepest meridian, the other half in a subsequent step a long the flattest meridian; thereafter, the spherical equivalent was correc ted. RESULTS: Six months postoperatively, mean spherical equivalent retraction w as -0.07 +/- 0.87 D and mean cylinder was -0.44 +/- 0.36 D. Mean spectacle- corrected visual acuity was 0.86 +/- 0.13 compared to 0.75 +/- 0.22 preoper atively. Mean corneal haze was 0.67 +/- 0.31. No patient lost 2 or more lin es of spectacle-corrected visual acuity and there were no complaints about night halos or glare. CONCLUSIONS: Unlike other ablation strategies, the cross-cylinder method cr eates a smooth transition (low dioptric gradient) between the treated and u ntreated cornea. This is achieved by first treating the cylinder and making the corneal surface spherical and then ablating the spherical component of the refractive error.