Meridian-Specific and Post-Optical Deficits of Spatial Vision in Human Astigmatism: Evidences From Psycho-Physical and EEG Scalings

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.

Traces of early developmental bias in the adult brain

“…4 ). The results show for most participants (controls and astigmatic individuals), as expected 20 , a higher sensitivity for the vertical meridian, but no correlation with the perceptual bias in the grouping task. Thus, the measured bias implies that the astigmatic individuals perceive the horizontal dimension compressed relative to the vertical dimension, thus perceiving a horizontal organization at the array’s equilibrium point.…”

Meridional binocular rivalry reveals a trace of uncorrected oblique input during development in the adult brain

“…Another study 15 showed that adaptation to astigmatic blur is transferred to long-term memory that could be engaged when blur is reapplied or disengaged when blur is removed. Gu et al 28 suggest that neural adaptation after long-term exposure may play a key role in compensating for optical blur. Accordingly, during the developmental period, the oblique astigmatic participant is continuously exposed to mirror symmetry oblique blur, which may induce monocular competition that may increase the BR episodes.…”

The Complex Treatment Effect on Meridional Visual Acuity Indicators in Patients With Astigmatism and Amblyopia

“…We used vernier visual acuity (VVA) indicators to evaluate the treatment methods. This indicator is one of the main criteria that allows you to assess the ability of the visual analyzer to analyze objects of complex configuration [4,23]. Special attention should be paid to forming homogeneous groups to exclude errors in assessing the results of amblyopia treatment in patients with astigmatism.…”

“…В результаті цього в оці одночасно існують два меридіани, в одному з яких ГЗ є вищою, ніж в іншому. Асиметрії рефракції, пов'язані з астигматизмом можуть бути причиною розвитку особливої форми амбліопії -меридіональної амбліопії (МА) [1,2,3,4,5]. МА проявляється селективним порушенням ГЗ при розрізненні контурів предметів певної орієнтації [3].…”

“…As a result, two meridians simultaneously exist in the eye, one of which has a higher VA than the other. Refraction asymmetries associated with astigmatism can be the reason for developing a particular form of amblyopia -meridional amblyopia (MA) [1,2,3,4,5]. MA is manifested by a selective violation of VA when distinguishing the contours of objects of a certain orientation [3].…”