Effects of Photorefractive Keratectomy on Higher-order Aberration and Contrast Sensitivity Function

Abstract

Abstract: : Purpose: To evaluate higher-order aberrations of the eye and contrast sensitivity function in patients undergoing excimer laser photorefractive keratectomy (PRK) for myopia. Methods: Ocular aberrations and contrast sensitivity function were determined before and 1 month after uneventful PRK in 56 eyes of 31 patients (mean age 31.6 +/- 11.7 years). Eyes with apparent corneal subepithelial haze after surgery were excluded from the subjects. Mean preoperative refractive error was -6.2 +/- 2.9D (range, -1.75 to 14D). Lower and higher order aberrations of the eyes were measured with a Hartmann-Shack wavefront aberrometer (Topcon KR-9000PW) for a 4-mm pupil, and Vector Vision CSV-1000 was used to assess area under the log contrast sensitivity function (AULCSF, 1000E), low contrast visual acuity (1000LanC10%), and letter contrast sensitivity (1000LV). Results: PRK significantly increased coma and spherical aberrations (paired t-test, p<0.0001). Best spectacle-corrected visual acuity did not change by surgery, but PRK induced significant reductions in AULCSF (p<0.001), low contrast visual acuity (p=0.001), and letter contrast sensitivity (p=0.020). The amount of myopic correction significantly correlated with postoperative coma (Pearson r=0.545, p<0.0001) and spherical (r=0.473, p<0.005) aberrations. Postoperative coma aberration correlated with AULCSF (r=-0.643, p<0.0001), logMAR low contrast visual acuity (r=0.674, p<0.0001), and letter contrast sensitivity (r=-0.680, p<0.0001). Postoperative spherical aberration showed significant correlation with AULCSF (r=-0.643, p<0.0001), logMAR low contrast visual acuity (r=0.457, p<0.001), and letter contrast sensitivity (r=-0.457, p<0.001). Conclusions: PRK increases ocular higher-order aberrations, which are thought to play a role in reducing contrast sensitivity function after surgery.

Keywords: refractive surgery: PRK • contrast sensitivity • cornea: clinical science