Improvement of Visual Acuity as An Aftereffect of Blur Adaptation through a Defocusing Lens

Our previous study has shown that blur adaptation through a foggy filter temporarily improved visual acuity (VA). Here we report the influence on VA from the adaptation to blurred images by a defocusing lens. In the experiment, a subject adapted to the blurred visual field by observing motion pictures through a trial lens either of 2.5D, 3.0D, 4.0D, or 5.0D. The visual acuity was measured in the periods of pre- and post-adaptation by a quick and simplified staircase method with Landolt C. The moment the lens was removed, subject's VA was obviously higher than the original VA and then gradually returned to the original level in a few minutes. However the degree of transient improvement in VA was not necessarily larger with longer period of adaptation. The enhancement in VA demonstrated here is presumably caused by blur adaptation and its aftereffect. The usual VA might not be the optimum performance of the hardware of an eye, or rather, be suppressed by the visual system in the level of the cortex.