Cortical visual processing differences in myopia and blur

Abstract

Myopia is projected to impact over 50 % of the global population by 2050. Despite links to long-lasting anatomical changes in visual cortices, little is known of potential consequences of myopia on visual brain functions, such as visual completion. We hypothesized that adults suffering from moderate myopia process attentionally demanding visual stimuli under optical blur differently than emmetropic adults. Non myopes (N = 12) and low-to-mild myopes (N = 13) were tested under −3 diopters of lens-induced blur. Participants performed an illusory contour discrimination task while 128-channel EEG was recorded. Each trial also included an intervening, task-irrelevant dartboard stimulus. Visual evoked potentials (VEPs) to the illusory contour (IC), no contour (NC), and dartboard stimuli were analyzed using an electrical neuroimaging framework. We provide evidence for cortical processing differences between non myopes and mild myopes at 218–280ms post-stimulus during visual completion, but not during viewing of dartboards. These differences stemmed from topographic modulations, indicative of the engagement of distinct networks of brain regions that were localized to medial portions of the occipital pole. Moreover, the predominant VEP topography during this time period both correlated with extent of refractive error, and also was an excellent classifier of myopia vs. emmetropia. By contrast, our analyses provided no evidence for differences in visual completion processes between groups. To our knowledge, this is the first study of myopia pairing high-density EEG and a behavioral task. Collectively, this pattern of findings supports a model of myopia wherein low-level visual cortices are impacted at relatively late post-stimulus processing stages.