Objective Measures of Retinal Image Degradation Due to Refractive Corrections.

Significance: There is a need for a measure, as simple and yet as informative as possible, to describe objectively the retinal image quality when a patient views targets at various distances through spectacle, contact, or intraocular corrections with optics more elaborate than single vision.

Purpose: The purposes of this study are to examine the current status of quantitative descriptions of retinal image blur and find optimal characterization of image degradation.

Methods: A variety of indexes of image degradation are computed for a typical eye and polychromatic light, in and out of focus, and as exemplars of sophisticated wave shaping, when the pupil transmission has been modified to a truncated Bessel amplitude function and to a "fractal" phase function.

Results: Figures are shown for the optical transfer, point- and edge-spread functions, and Koenig bar and optotype letter blur for the various imaging and defocus conditions, and the relative values of several blur indexes are compared graphically and in a correlation table.

Conclusions: No single index captures the many ways in which the image can deviate from the diffraction-limited ideal. Among the incomplete descriptors of image degradation, the light distribution at a sharp edge stands out as optimally informative and economical, and, when condensed to just two values, one representing central image sharpness and the other outlying light spread, allows for a quick survey of the imaging deficit.