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Open AccessArticle

Long-Range Interocular Suppression in Adults with Strabismic Amblyopia: A Pilot fMRI Study

1
School of Optometry and Vision Science, University of Waterloo, Waterloo, ON N2L 3G1, Canada
2
McGill Vision Research, Department of Ophthalmology and Visual Sciences, McGill University, Montreal, QC H4A 3S5, Canada
3
School of Optometry and Vision Science, University of Auckland, Auckland 1142, New Zealand
4
Department of Human Sciences, Kanagawa University, Yokohama 221-8686, Japan
5
Department of Ophthalmology, University of Manitoba, Winnipeg, MB R3T 2N2, Canada
*
Author to whom correspondence should be addressed.
Received: 7 November 2018 / Revised: 15 December 2018 / Accepted: 31 December 2018 / Published: 8 January 2019
(This article belongs to the Special Issue Visual Perception and Its Neural Mechanisms)
Interocular suppression plays an important role in the visual deficits experienced by individuals with amblyopia. Most neurophysiological and functional MRI studies of suppression in amblyopia have used dichoptic stimuli that overlap within the visual field. However, suppression of the amblyopic eye also occurs when the dichoptic stimuli do not overlap, a phenomenon we refer to as long-range suppression. We used functional MRI to test the hypothesis that long-range suppression reduces neural activity in V1, V2 and V3 in adults with amblyopia, indicative of an early, active inhibition mechanism. Five adults with amblyopia and five controls viewed monocular and dichoptic quadrant stimuli during fMRI. Three of five participants with amblyopia experienced complete perceptual suppression of the quadrants presented to their amblyopic eye under dichoptic viewing. The blood oxygen level dependant (BOLD) responses within retinotopic regions corresponding to amblyopic and fellow eye stimuli were analyzed for response magnitude, time to peak, effective connectivity and stimulus classification. Dichoptic viewing slightly reduced the BOLD response magnitude in amblyopic eye retinotopic regions in V1 and reduced the time to peak response; however, the same effects were also present in the non-dominant eye of controls. Effective connectivity was unaffected by suppression, and the results of a classification analysis did not differ significantly between the control and amblyopia groups. Overall, we did not observe a neural signature of long-range amblyopic eye suppression in V1, V2 or V3 using functional MRI in this initial study. This type of suppression may involve higher level processing areas within the brain. View Full-Text
Keywords: visual development; binocular vision; functional magnetic resonance imaging; strabismus; visual processing; primary visual cortex visual development; binocular vision; functional magnetic resonance imaging; strabismus; visual processing; primary visual cortex
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Thompson, B.; Maehara, G.; Goddard, E.; Farivar, R.; Mansouri, B.; Hess, R.F. Long-Range Interocular Suppression in Adults with Strabismic Amblyopia: A Pilot fMRI Study. Vision 2019, 3, 2.

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