Abstract
Previous studies have demonstrated that orientation-specific deprivation in early life can lead to neural deficits of spatial vision in certain space, and can even result in meridional amblyopia (MA). Individuals with astigmatism are the optimal and natural models for exploring this asymmetric development of spatial vision in the human visual system. This study aims to assess the contrast sensitivity function (CSF) and EEG signals along two principal meridians in participants with regular astigmatism when being optimal optical corrected. Twelve participants with astigmatism (AST group, 20 eyes) and thirteen participants with (MA group, 19 eyes) were recruited in the current study. CSFs and spatial sweep visual evoked potentials (sVEP) were measured with vertical and horizontal sinewave gratings along two principal meridians monocularly. Area under log CSF (AULCSF), spatial frequency threshold corresponding to 80% contrast gratings (SF threshold at 80% ctr), and CSF acuity were calculated from CSF test. In addition, sVEP amplitudes and thresholds were calculated with the recursive least square method. Participants with astigmatism exhibited marked vertical-horizontal resolution disparities even after they were corrected with optimal optical corrections. CSF tests showed that AULCSF along weak meridian (measured with horizontal gratings) was lower than that along strong meridian (measured with vertical gratings) in both groups. Significant meridional disparity of CSF acuity was also found in both groups. In addition, the MA group showed larger meridional disparity compared to the AST group. Spatial sVEP thresholds also supported the existence of marked meridional disparity. Our results suggest that meridian-specific partial deprivation in early life might lead to monocularly asymmetric development of spatial vision in the human visual system. In terms of application, we tested the feasibility and reliability of adopting psychophysical and EEG scalings to investigate the asymmetric development of spatial vision related to astigmatism. These paradigms are potentially applicable to reduce and even eliminate the meridional disparity in the primary visual cortex by adopting perceptual learning or other vision-related interventions.
Highlights
The development of visual system is extraordinary sensitive to early visual experience (Berardi et al, 2000; Knudsen, 2004; Kiorpes, 2016)
The Area under log contrast sensitivity function (CSF) (AULCSF), spatial frequency threshold corresponding to 80% contrast gratings (SF threshold at 80% ctr), and CSF acuity were calculated from CSF tests, and the sweep visual evoked potentials (sVEP) thresholds were calculated to evaluate meridional disparity in spatial acuity
The current study investigated the asymmetric development of spatial vision related to astigmatism in the human visual system via combining psycho-physical and EEG scalings
Summary
The development of visual system is extraordinary sensitive to early visual experience (Berardi et al, 2000; Knudsen, 2004; Kiorpes, 2016). Abnormal visual experience will result in functional and structural deficits in the visual pathway and cerebral cortex, such as deprivation amblyopia (Kiorpes and McKee, 1999; Kiorpes, 2006). Psychophysical, electrophysiological, and neuro-imaging techniques make the exploration of neural mechanism underlying human amblyopia feasible and fruitful. Animal studies have consistently demonstrated that visual deprivation along one orientation would lead to orientation-specific deficits in the visual pathway and cerebral cortex (Blakemore and Cooper, 1970; Hirsch and Spinelli, 1970). Systematic and comprehensive investigation of meridian-specific deficits in the human visual system is still lacking
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