Effect of induced anisometropia on binocular through-focus contrast sensitivity

The aim of this study was to characterize binocular through-focus function in white light and to investigate the effect of induced anisometropia on binocular depth of focus.

The subjects viewed sine-wave gratings generated on a monitor through a modified Badal system that produced gradual changes in target vergence ranging from -4.00 to +2.00 D. Binocular through-focus contrast sensitivity curves were obtained at a spatial frequency of 11 cpd and for different levels of induced anisometropia. Subjective depths of focus were derived from the through-focus curves.

An induced anisometropia lower than 1.00 D led to a monomodal through-focus curve involving a single depth of focus, whereas with higher anisometropia, the curves became bimodal indicating a lack of performance at intermediate distance. Binocular thresholds predicted by the quadratic summation model from our monocular measurements were well correlated to our binocular measurements. Predictions allowed us to estimate optimum levels of induced anisometropia.