CORNEAL OPTICAL IRREGULARITY AFTER EXCIMER-LASER PHOTOREFRACTIVE KERATECTOMY

Purpose: To assess the influence of corneal surface microirregularitie s on objective and subjective visual performance after photorefractive keratectomy (PRK). Setting: Multicenter clinical trial. Methods: The alpha version of the Potential Corneal Acuity (PCA) computer program, currently under development, was used to qualitatively and quantitativ ely analyze the corneal surface of 176 eyes of 176 patients 1 year aft er PRK. Color maps of corneal surface irregularities were reviewed and quantitative values (PCA) predicting best spectacle-corrected visual acuity (BSCVA) as limited by the cornea were evaluated for association s with qualitative topography patterns, optical zone decentration, and clinical outcomes of BSCVA, uncorrected visual acuity (UCVA), subject ive patient satisfaction, and a subjective glare/halo index. Results: Qualitatively, corneas after PRK were generally characterized by a rin g of optical irregularity at the juncture of the ablation zone and unt reated cornea, Standard corneal topography maps graded as irregular af ter PRK had a significantly higher PCA value than those graded as regu lar. There was a trend toward higher PCA values with greater optical z one decentration that was not statistically significant. Actual BSCVA was identical to that which the PCA value predicted in 32% of patients and was within one Snellen line in 71%, within two lines in 89%, and within three lines in 94%. The correlation between the PCA and the gla re/halo index and with subjective patient satisfaction was statistical ly significant. The relationship between PCA and UCVA was not signific ant. Conclusions: A ring of optical microirregularity of the corneal s urface can appear at the juncture of the treated and untreated cornea after PRK, indicating that the optical zone edge might affect objectiv e and subjective postoperative visual outcomes. Further understanding of corneal surface topography and refinement of the PCA program should help explain visual outcome after PRK.