Corneal asphericity following excimer laser photorefractive keratectomy. Summit PRK Topography Study Group

Abstract

Background and objective: To analyze corneal asphericity following excimer laser photorefractive keratectomy (PRK) and its influence on clinical outcomes.

Patients and methods: A computer program (Holladay Diagnostic Summary, EyeSys Laboratories, Houston, TX) was used to qualitatively and quantitatively analyze the corneal asphericity of 132 patients 1 year following PRK for correction of myopia. Color maps depicting actual corneal asphericity as compared to the normal expected asphericity were reviewed, and quantitative values of asphericity were evaluated for associations with clinical outcomes of uncorrected visual acuity and spectacle corrected visual acuity, achieved refractive correction, a subjective glare/halo index, and subjective patient satisfaction, as well as standard corneal topography patterns and optical zone decentration following PRK.

Results: Following PRK, all corneas exhibited a positive central asphericity, changing from a prolate (negative asphericity) to an oblate optical contour. There was a trend toward higher positive asphericity measurements with improving spectacle corrected visual acuity which was not statistically significant; such a relationship was not found with uncorrected visual acuity. A significant association was found between greater achieved refractive correction and increased postoperative positive asphericity. No association was found between postoperative asphericity and the glare/halo index, subjective patient satisfaction, topography pattern, or optical zone decentration.

Conclusion: Asphericity may be a useful quantitative descriptor of corneal optical contour following PRK. Greater positive central corneal asphericity is found with greater degrees of refractive correction. Further understanding of both the pre- and post-operative corneal contour and the consequent optical effects should aid in a better understanding of the optical outcomes of PRK.