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Benjamin Thompson, Goro Maehara, Reza Farivar, Behzad Mansouri, Simon Clavagnier, Robert Hess; Interocular suppression within the visual cortex of adults with strabismic amblyopia: an fMRI study. Invest. Ophthalmol. Vis. Sci. 2013;54(15):3994. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
There is increasing evidence that interocular suppression plays a key role in the visual deficits experienced by patients with amblyopia. The aim of this study was to assess whether suppression of inputs from the amblyopic eye occurs within the primary and/or extrastriate visual cortex of adult patients with strabismic amblyopia.
Five adult patients (mean age 34 years) with strabismic amblyopia (acuity range 20/50 to 20/160) and 5 control observers took part in this study. During fMRI, participants viewed dichtopic, suprathreshold, sinusoidal grating stimuli (30% contrast, 0.5cpd) with one grating presented to each quadrant of the visual field. Following a block design, the four quadrants were either presented monocularly to one eye or dichoptically with two quadrants presented to each eye. The latter condition was designed to activate suppression of the amblyopic eye. Retinotopic maps were obtained for each patient and the regions of the cortical surface in V1, V2 and V3 that corresponded to each quadrant of the visual stimulus were identified. BOLD data were analyzed separately for each patient for each region of interest using a general linear model. Psychophysical measurements were also made using a suprathreshold matching procedure to assess the strength of suppression evoked by dichoptic stimulus presentation.
Psychophysical measurements indicated that three patients completely suppressed the quadrants presented to the amblyopic eye under dichoptic viewing conditions. For the remaining patients, one experienced weak suppression and the other experienced contrast enhancement of the suprathreshold stimuli presented to the amblyopic eye. The three patients with strong suppression showed a significantly reduced BOLD response in the regions of V1 (2 patients), V2 (2 patients) and V3 (2 patients) driven by the amblyopic eye under dichoptic viewing conditions. No reliable changes were found for the patient with weak suppression and the patient with contrast facilitation showed a significant increase within the regions of V2 driven by the amblyopic eye.
Strong suppression of the amblyopic eye is associated with a reduced BOLD response in regions of the striate and extrastriate cortex in adults with strabismic amblyopia.
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