Variability of the refractive state: meridional profiles and uniform variation

Variation of the refractive state as measured with autorefraction is the result of many factors which need to be considered if optometry is to develop a more complete understanding of the behavior of the visual process. Various methods can be applied to develop such an understanding including scatter plots, meridional profiles of variance-covariance, and graphs of uniform variation. These methods are used, in this paper, to investigate some results for autorefraction from a sample of 106 university students studying optometry. Some of the eyes in the sample display variation, some or all of whose characteristics are the same in all meridians of the eye. Such eyes are said to exhibit refractive variation that is partially or completely uniform across the meridians of the eye. Most eyes, however, show variation which appears to depart from uniformity. The typical eye in the sample appears to exhibit variation that is mainly spherical in character and of a small magnitude in keeping with the view that the accommodative system mostly is responsible for this variation. Nevertheless, there is an astigmatic component to the variation. The mean variance-covariance matrices for the right and left eyes are presented.