Spherocylindrical refractive errors and visual acuity

Understanding the relation between refractive error and visual acuity is complicated if astigmatic blur is present. No models are in widespread use that allow the combination of spherical and astigmatic errors for the purpose of predicting visual performance.

Models for combining spherical and astigmatic errors are discussed, and predictions of these models using data from the literature are presented.

Three models for combining astigmatic with spherical errors are shown to predict visual acuity performance in uncorrected myopic refractive errors. A dioptric vector addition model is shown to have advantages over other candidate models.

It is possible to combine spherocylindrical refractive errors into a single value when the objective is to correlate these values with visual acuity performance.