Abstract
Abstract: :
Purpose: Previous studies have demonstrated a significant improvement in visual resolution during sustained periods of retinal blur. This appears to result from perceptual adaptation designed to restore the perceived contrast of the degraded retinal image. However, it is unclear whether this perceptual adaptation 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 blur adaptation in both emmetropic and myopic individuals. Methods: Two experiments will be described. Firstly, the effects of sustained retinal blur on both high and low contrast visual resolution was compared in emmetropes (N=12) and myopes (N=16). Subjects were required to view through +2.50D spherical lenses worn over their distance refractive correction for a continuous 2-hour period. Secondly, 20 subjects having moderate degrees of myopia (mean refractive error = -2.07D) spent 3 hours without any refractive correction, during which time they watched television at a viewing distance of 4m. High contrast visual acuity and contrast sensitivity were measured using randomized logMAR charts and a B-VAT computerized display, respectively. Both studies also included a control condition, whereby repeated measurements of visual resolution were made while subjects were fully corrected. Results: In the first study a significant improvement in visual acuity was observed in both refractive groups. However, there was no significant difference between the levels of adaptation observed in the emmetropic and myopic groups. The mean improvement in high contrast acuity was from 0.78 to 0.59 logMAR units (p=0.04). In the second experiment, mean uncorrected acuity improved from 0.76 to 0.53 logMAR units (p=0.0001). Additionally, significant improvements in resolution were observed across contrast levels ranging from 2.5 to 40%. The improved acuity was not accompanied by any significant change in refractive error. Furthermore, no significant change in visual resolution was observed in the corrected control groups. Conclusion: These results demonstrate significant blur adaptation, which does not result from a change in refractive state. We hypothesize that the improvement in visual resolution results from perceptual adaptation to the blurred image, which may occur at central sites within the visual cortex.
Keywords: 620 visual acuity • 542 refraction • 481 myopia