Treatment of post-keratoplasty astigmatism by topography supported customized laser ablation

Purpose: To evaluate the clinical and optical efficiency of topography modu lated customized corneal ablations for irregular corneal astigmatism. Material & methods: Sixteen eyes of 16 patients with iatrogenic corneal ast igmatism (post keratoplasty) were consecutively included. Based on preopera tive corneal topographic measurements height deviations from a spherical co rneal shape were calculated and transferred to a flying-spot excimer laser. Photorefractive keratectomy of the topographic irregularities was then per formed. Clinical and optical efficiency was evaluated by best corrected vis ual acuity and by computation of corneal wavefront aberrations before and u p to one year after treatment. Wavefront aberrations were decomposed by Zer nike polynomial analysis. Results: Before treatment the average best-corrected visual acuity was 0.23 . Three and 12 months after PRK the average best-corrected visual acuity ha d increased to 0.37 (p<0.05) and 0.45 (p<0.05), respectively. Corneal wavef ront aberrations (root-mean-square) were 3.35 before surgery and 1.88 (p<0. 05) and 1.51 (p<0.05) at three and 12 months after treatment. Zernike polyn omial decomposition of the wavefront aberrations revealed that regular corn eal astigmatism was the most important aberration component before and afte r surgery. Regular astigmatism was significantly decreased by the procedure , whereas coma, spherical aberrations, and higher-order aberrations were no t reduced significantly. Conclusion: Topography modulated photorefractive keratectomy of highly asti gmatic corneal grafts can improve best corrected visual acuity and reduce c orneal wavefront aberrations. Even in apparently irregular topographic asti gmatism, regular astigmatic wavefront aberration may be the most important contributor to wavefront errors.