EVALUATING SURGICALLY INDUCED ASTIGMATISM BY FOURIER-ANALYSIS OF CORNEAL TOPOGRAPHY DATA

Purpose: To evaluate surgically induced astigmatism using Fourier harm onic series analysis of corneal topography data. Setting: Aarhus Kommu nehospital, Aarhus University, Denmark. Methods: We evaluated the resu lts of 46 phacoemulsifications with a 4 or 6 mm scleral tunnel suturel ess incision based on the axis of the steepest meridian. We performed conventional keratometry and corneal topography before and up to 1 mon th after surgery. Using Fourier analysis, the corneal topographic imag es were broken into spherical power, regular astigmatism, and nonregul ar astigmatism for individual or aggregate analysis of surgically indu ced astigmatism. The induced refractive change (average of the differe nce between preoperative and postoperative corneal topographies) was a nalyzed and normalized according to the surgical meridian and to right /left eye. Results: Regular astigmatism calculated by Fourier analysis of mires from the keratometer zone correlated well with conventional keratometry readings. Surgery induced a localized flattening in the su perior region and a with-the-rule regular astigmatism component in the central area. Conclusion: Surgically induced corneal topography chang es can be analyzed by Fourier series harmonic analysis, allowing aggre gate data to be broken into optically meaningful quantities.