The Effect of Contrast Reversal on Peripheral Visual Acuity.

PURPOSE: Patients with central vision loss must rely upon regions of their unaffected peripheral retina to carry out fine-scale visual tasks. We aimed to determine the conditions under which contrast reversal of targets and/or backgrounds may act to improve visual acuity in the peripheral field.

METHODS

Ten participants with normal or corrected-to-normal vision performed a visual acuity task in which they were asked to identify the orientation of a letter-C target presented at 10° in the right visual field. Minimum letter size thresholds were measured for static (black or white) and contrast-reversing (8.5 or 17 Hz) targets presented on a uniform mean luminance background, a static patterned background, or a dynamic version of the patterned background, which was contrast reversing at the same temporal frequencies used for the targets.

RESULTS

When presented on a uniform background, black targets produced lower thresholds than white targets, and there was no consistent benefit of contrast reversal. However, when presented on a patterned background, acuity for contrast-reversing targets consistently exceeded that for either polarity static target. Contrast reversing the background also improved acuity, for both static targets and targets that contrast reversed at a different rate.

CONCLUSIONS

Peripheral visual acuity is significantly enhanced by dynamic contrast modulation, particularly when the modulation acts to promote segmentation between target and background.

TRANSLATIONAL RELEVANCE: Adding temporal modulation to the target or background could provide a simple way of enhancing peripheral acuity for patients with central vision loss.