The forgotten tract of vision in multiple sclerosis: vertical occipital fasciculus, its fiber properties, and visuospatial memory

Visual disturbances are a common disease manifestation in multiple sclerosis (MS) due to lesions damaging white matter tracts involved in vision. Vertical occipital fasciculus (VOF), a tract located vertically in the occipital lobe, was neglected for more than a century. We hypothesize that VOF is involved in integrating information between dorsal and ventral visual streams. Thus, its damage in MS, as well as its probable role in visual processing (by using MS as a VOF damage model) needs to be clarified. To study fiber characteristics of VOF in MS, and their clinical and visual learning associations, 57 relapsing-remitting MS (RRMS) and 25 healthy controls (HC) were recruited. We acquired MS Functional Composite, Expanded Disability Status Scale (EDSS), and Brief Visuospatial Memory Test-Revised (BVMT-R), and diffusion MRI scans. Tractography of VOF and optic radiation (OR) was done. VOF's metrics were statistically tested for between-group differences and clinical and visual tests associations. Along-tract analysis and laterality were also tested. RRMS patients had higher mean, axial, and radial diffusivity (nearly in all fiber points), and lower fractional anisotropy in bilateral VOFs compared to HC. No laterality was noted. These were associated with poor clinical outcomes, poor visual scores in EDSS, and lower total immediate and delayed recall in BVMT-R in RRMS, after adjusting for age, gender, and fiber metrics of OR. VOF damage is present in RRMS and is associated with visual symptoms and visuospatial learning impairments. It seems VOF is involved in integrating information between visual streams.