Objective: To investigate the role of the superior colliculus (SC) using functional brain MRI (fMRI) and a visual stimulation paradigm based on luminance contrast variations in people with idiopathic blepharospasm (BSP) compared to controls.

Background: Etiology and pathophysiology of idiopathic BSP are still largely unknown. It has been hypothesized that BSP is the consequence of a dysfunction of the basal ganglia loop, although cortical areas and other brainstem structures may be involved. fMRI is a suitable tool for a non-invasively investigation of such cortical and subcortical dysfunctions. To date, no fMRI data in specific brainstem regions in BSP patients has been reported.

Method: People with idiopathic BSP and controls were recruited. All participants underwent brain fMRI using a recently published standardized protocol. Thus paradigms allows to modulate the activity in the first steps of visual processing and record the corresponding blood oxygenation level–dependent (BOLD) signal in the SC, the lateral geniculate nucleus (LGN), and the primary visual cortex (V1).

Results: In ten BSP patients, there was no modulation of the SC responses to the luminance contrast variations (1 to 9%) compared to ten controls, supporting a hypersensitivity to low luminance contrast (1%) and abnormal rapid BOLD signal saturation to higher luminance contrasts. The LGN was only weakly modulated by 3 to 9% luminance contrasts compared to controls. No major differences were found in the V1 between groups. Overall, the BOLD signal was lower in these three structures in people with BSP compared to controls.

Conclusion: Our findings support a dysfunction of the SC in idiopathic BSP. Brain fMRI targeting visual structures like the SC could play an important role as a biomarker of the disease.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/visual-dysfunction-of-the-superior-colliculus-in-idiopathic-blepharospasm-a-pilot-study/