New Objective Refraction Metric Based on Sphere Fitting to the Wavefront

PURPOSE: To develop an objective refraction formula based on the ocular wavefront error (WFE) expressed in terms of Zernike coefficients and pupil radius, which would be an accurate predictor of subjective spherical equivalent (SE) for different pupil sizes. METHODS: A sphere is fitted to the ocular wavefront at the center and at a variable distance, t. The optimal fitting distance, t(opt), is obtained empirically from a dataset of 308 eyes as a function of objective refraction pupil radius, r(0), and used to define the formula of a new wavefront refraction metric (MTR). The metric is tested in another, independent dataset of 200 eyes. RESULTS: For pupil radii r(0) ≤ 2 mm, the new metric predicts the equivalent sphere with similar accuracy (<0.1D), however, for r(0) > 2 mm, the mean error of traditional metrics can increase beyond 0.25D, and the MTR remains accurate. The proposed metric allows clinicians to obtain an accurate clinical spherical equivalent value without rescaling/refitting of the wavefront coefficients. It has the potential to be developed into a metric which will be able to predict full spherocylindrical refraction for the desired illumination conditions and corresponding pupil size.