Wavefront properties of the anterior and posterior corneal surface after photorefractive keratectomy.

Purpose: The aim of this study was to evaluate the balance and changes of corneal higher order aberrations (HOAs) after photorefractive keratectomy (PRK).
Methods: Myopic and myopic-astigmatic patients (89 eyes of 48 patients) were enrolled in this study. A PRK was performed using an Asclepion Meditec MEL 80 G flying-spot excimer laser. The mean ablation depth and diameter were 76.78 μm (±19.40 μm) and 6.0 mm (±0.06 mm), respectively. Before and 1 year after the surgery, uncorrected and best spectacle-corrected visual acuities were determined. Wavefront aberrations of the anterior [root mean square (RMS)-HOA anterior], posterior (RMS-HOA posterior), and total cornea (RMS-HOA total) were measured using a Scheimpflug Camera. Linear piecewise regression analysis was used for correlations between the ablation depth and aberration of the anterior corneal surface. The follow-up time was 1 year.
Results: At baseline, RMS-HOA anterior proved to be significantly higher compared with RMS-HOA total (P < 0.001). After the PRK was performed, the RMS-HOA anterior (P < 0.001) and RMS-HOA total values (P < 0.001) increased significantly; however, RMS-HOA posterior values (P = 0.12) remained stable. Above an ablation depth of 76.78 μm, the RMS-HOA anterior increased 2.4-fold. Uncorrected and best spectacle-corrected visual acuities were 1.0 (20/20) in 95.5% and 98.8% of the patients 1 year postoperatively.
Conclusions: Aberrations of the posterior corneal surface seem to compensate for wavefront alterations of the anterior cornea, decreasing the amount of wavefront error regarding the total cornea in myopic patients. PRK induced increased HOAs with respect to the anterior corneal surface; however, the posterior surface remained stable. The increase in the HOAs was measured to be significantly larger above 76.78 μm photoablation depth.