Linking Multi-Modal MRI to Clinical Measures of Visual Field Loss After Stroke

Abstract

Loss of vision across large parts of the visual field is a common and devastating complication of cerebral strokes. In the clinic, this loss is quantified by measuring the sensitivity threshold across the field of vision using static perimetry. These methods rely on the ability of the patient to report the presence of lights in particular locations. While perimetry provides important information about the intactness of the visual field, the approach has some shortcomings. For example, it cannot distinguish where in the visual pathway the key processing deficit is located. In contrast, brain imaging can provide important information about anatomy, connectivity, and function of the visual pathway following stroke. In particular, functional magnetic resonance imaging (fMRI) and analysis of population receptive fields (pRF) can reveal mismatches between clinical perimetry and maps of cortical areas that still respond to visual stimuli after stroke. Here, we demonstrate how information from different brain imaging modalities—visual field maps derived from fMRI, lesion definitions from anatomical scans, and white matter tracts from diffusion weighted MRI data—provides a more complete picture of vision loss. For any given location in the visual field, the combination of anatomical and functional information can help identify whether vision loss is due to absence of gray matter tissue or likely due to white matter disconnection from other cortical areas. We present a combined imaging acquisition and visual stimulus protocol, together with a description of the analysis methodology, and apply it to datasets from four stroke survivors with homonymous field loss (two with hemianopia, two with quadrantanopia). For researchers trying to understand recovery of vision after stroke and clinicians seeking to stratify patients into different treatment pathways, this approach combines multiple, convergent sources of data to characterize the extent of the stroke damage. We show that such an approach gives a more comprehensive measure of residual visual capacity—in two particular respects: which locations in the visual field should be targeted and what kind of visual attributes are most suited for rehabilitation.

Volume and Visual Field Defects in Occipital Stroke: The NOR-OCCIP Study

“…A large number of patients with AIS in the visual pathways had involvement of one or more of the areas 1-6 in the primary visual cortex (81%), but the majority also had additional involvement of at least one of the areas 7-14. Beh [9]. Visual field maps were derived from fMRI, the lesions were delineated on anatomical scans, and white matter tracts from diffusionweighted MRI data.…”

“…Previous studies have confirmed the retinotopic map of the human occipital cortex by correlating magnetic resonance imaging (MRI) findings with visual field defects in patients with occipital lobe infarcts [6,7]. However, only a few studies attempt to correlate the exact lesion location and volume with visual field defects and file prognosis in patients with acute occipital infarcts [8,9]. We wanted to examine this closer in a Norwegian population.…”