Blur adaptation and myopia.
Previous studies have demonstrated a significant improvement in visual resolution during sustained periods of retinal defocus. This appears to result from perceptual adaptation designed to restore the perceived contrast of the degraded image. However, it is unclear whether perceptual adaptation to sustained blur is present in all individuals or only in certain subgroups, such as those who have been chronically exposed to sustained periods of blur due to uncorrected ametropia. Accordingly, the present study examined the effects of sustained retinal defocus on both high-and low-contrast visual acuity in emmetropes (n = 13) and myopes (n = 18). Subjects were required to view through +2.50-D spherical lenses worn over their distance refractive correction for a continuous 2-hour period. A significant improvement in both Landolt C and grating visual acuity measured through the fogging lenses was observed in both refractive groups. Although the mean change in grating visual acuity was significantly greater for the myopic subjects, the improvements in Landolt C acuity observed in the emmetropes and myopes were statistically equivalent. We hypothesize that the improvement in visual acuity results from perceptual adaptation to the blurred images, which may occur at central sites within the visual cortex.