Does blur adaptation transfer between eyes?

Purpose How the eye detects and responds to blur is a fundamental question for myopia research. The mechanisms through which the eye partially adapts to blur and shows improvement in visual acuity over time is unknown. If a local retinal mechanism is responsible for blur adaptation, then we would not predict an interocular transfer of the blur adaptation. Methods Eighteen young adults (mean age of 22 yrs, 10 emmetropes and 8 myopes) participated in the study. The subjects were optimally corrected watching a movie at 5 m for 30 minutes while exposed to +2 D blur in the right eye while the left eye was clear. Visual acuity was measured with a high contrast projected logMAR chart at 5 m in photopic conditions with random letter sequences to avoid learning effects, both at the start of blur exposure, and following 30 mins of continuous blur exposure. In one trial the right eye was tested at the start, and immediately after the 30 mins of +2 D blur exposure, and in a second trial on another day, the left eye (clear during the 30 mins) was tested at the start and end of 30 mins with +2 D blur (Figure 1). The order of testing was randomized. Results Visual acuity of the right (blurred) eye changed from 0.73 +/- 0.04 logMAR to 0.67 +/- 0.03 logMAR after 30 mins of viewing through the defocus, representing a small improvement of visual acuity of 0.06 +/- 0.03 logMAR. The fellow left (clear) eye changed from 0.70 +/- 0.03 logMAR to 0.71 +/- 0.03 logMAR after 30 mins representing a negligible change of visual acuity of 0.01 +/- 0.02 logMAR. Improvement in visual acuity after blur adaptation in the right (blurred) eye was significant (p = 0.04), while the change in the left (clear) eye visual acuity was not significant (p = 0.8). Conclusions A small amount of blur adaptation in the blurred right eye after 30 min of +2 D blur, as expected. However no change in the visual acuity of the clear fellow eye when tested with +2 D blur, indicating no interocular transfer of blur adaptation. Suggests the mechanism of blur adaptation may be occurring locally within the eye experiencing the blur and not at a cortical level