Preserved motion perception and the density of cortical projections to V5 in homonymous hemianopia

Abstract

Abstract Following a unilateral post-chiasmal lesion of the geniculo-striate pathway, patients develop homonymous visual field defects. Using classical perimetry, patients with “complete” homonymous hemianopia are unaware of stimuli in the affected hemifield. However, some show residual vision in the affected hemifield in which the conscious perception of moving stimuli is preserved (Riddoch Phenomenon). Prior evidence suggests that preservation of a direct pathway from the lateral geniculate nucleus to visual area 5 (bypassing the primary visual cortex) may be the basis of this type of residual vision. The aim of the present study was to investigate the possibility of a correlation between preserved motion perception in hemianopia and the fibre connectivity density of the underlying pathways. This research was a case-control study carried out in a tertiary care centre between 2019 and 2021. Participants (n=48) were divided into two groups: patients with homonymous visual field defects (n=20) and normal controls (n=28). All participants underwent Humphrey field analysis (outcome=visual field index); kinetic perimetry (outcome=%correct); brain MRI; and diffusion tensor imaging probabilistic tractography (outcome=fibre connectivity density). The difference between %correct in kinetic perimetry and visual field index in Humphrey field analysis provided an indication of the level of preserved motion perception. A significant positive correlation was found between the fibre connectivity density of contralateral lateral geniculate nucleus-contralateral visual area 5 and the preserved motion perception (rho=0.5965, P<0.0012) and between the fibre connectivity density of contralateral visual area 5-contralateral lateral geniculate nucleus and the preserved motion perception (rho = 0.5635, P <0.0012) after adjusting with the Bonferroni method. The area under the curve was 0.7947 for the preserved motion perception in reflecting the fibre connectivity density of contralateral lateral geniculate nucleus-contralateral visual area 5, and 0.7660 for the preserved motion perception in reflecting the fibre connectivity density of contralateral visual area 5-contralateral lateral geniculate nucleus. We have demonstrated an extensive network of pathways connecting visual areas in the two hemispheres via the splenium of the corpus callosum. To our knowledge, this is the first report of a correlation between the preserved motion perception and the fibre connectivity density of the pathways underlying the Riddoch Phenomenon (specifically bilateral lateral geniculate nuclei to visual area 5 contralateral to the lesion). The difference between % correct in kinetic perimetry and visual field index measures the preserved motion perception and is related to the underlying neural damage. The methodology has the potential to evaluate and monitor patients with hemianopia.