Fourier analysis of corneal astigmatic changes following photorefractive keratectomy

The purpose of this study was to evaluate the corneal irregular astigmatism following photorefractive keratectomy (PRK) for myopia. The corneal topography of 30 eyes of 26 patients was measured with the TMS-1 videokeratoscope before and 1 month after PRK. Axial dioptric data were decomposed into four components; A0 (Sphericity), C1 × 2 (Asymmetry), C2 × 2 (Regular astigmatism), and C3 (higherorder irregularity) for the central 3 and 6 mm zone by Fourier series harmonic analysis. Post-operative topographies were divided into those with an irregular and those with a homogeneous pattern, and the Fourier components were compared. In the 6mm zone, A0 was significantly decreased (P < 0.001), and C1 × 2, C2 × 2, and C3 were significantly increased (P = 0.001, 0.005, 0.002, respectively). In the 3mm zone, A0 decreased (P < 0.001) and C1 × 2 increased (P < 0.001) significantly. C1 × 2 was correlated with the post-operative corrected visual acuity (P < 0.001, r = 0.647). The irregular pattern group had a larger C1 × 2 component (P < 0.001). The treatment displacement was not correlated with any component. In conclusion, irregular topography due to intraoperative drift or asymmetrical wound healing may play a more important role in the post-operative corneal optical property than mild treatment displacement.