A study on homonymous visual field deficits using brain imaging and simulations

Beh, Anthony (2023) A study on homonymous visual field deficits using brain imaging and simulations. PhD thesis, University of Nottingham.

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Homonymous visual field deficit (HVFD) is a common and devastating complication of cerebral strokes. This impairment has a dramatic impact on quality of life, disrupting multiple facets of daily life – most notably reading fluency. At present, there are no universally accepted, effective rehabilitation programs for HVFD. The most promising strategies involve repetitive visual stimulation in the ‘blind’ field using a broad range of stimuli to perceptually “retrain” visual function. Although effectiveness of this approach varies substantially, it could be because the most appropriate areas of the field are not targeted or the stimulus used in training is not optimized for each patient. A major issue in rehabilitating HVFD is the heterogeneity across individuals, where there is variability in lesion size, location, time since lesion, and most importantly the pattern of residual visual capacity. The potential for recovery may be limited to individuals with intact cortical structures or alternative visual pathways that could support some level of visual reorganization.

To address this issue, this thesis discusses the use of a cross-modal imaging approach to characterize HVFD, complementing standard visual assessments and perimetry with high-resolution definitions of patient-specific patterns of residual visual field coverage and cortical integrity. Here I present detailed perimetry and brain imaging datasets from 4 stroke survivors with HVFD (2 with hemianopia, 2 with quandrantanopia). My data reveals mismatches between the perimetry and functional responses mapped using functional magnetic resonance imaging (fMRI), revealing robust measures of residual visual capacity in the ‘blind’ field for all stroke survivors. I also used a probabilistic atlas to link functional activity to defined anatomical regions as well as major white matter tracts from probabilistic tractography. Taken together, this information provides a useful platform for a personalized approach to therapy – guided by functional activity patterns in the post-stroke brain.

Building on the idea of restoring visual function, this thesis also explores how recovery in the blind field can address reading impairments caused by HVFD. By visually manipulating an image in a single hemifield with a low-pass spatial filter under a gaze contingent paradigm, I could functionally simulate hemianopia. This also allowed me to systematically degrade spatial information in the hemianopic field and make inferences about the extent of visual field recovery required via restitutive HVFD strategies to restore functional reading performance. Consequently, this experiment also acts as a starting point to explore effects of visual restoration on reading with HVFD and allows us to test new strategies in healthy controls, before translating to patient groups.

Finally, this thesis outlines potential future directions for this line of investigation. These ideas include the development of rehabilitative strategies guided by patient-specific information using cross-modal imaging and testing out different configurations of visual manipulation in the simulated hemianopia design.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Schluppeck, Denis
McGraw, Paul
Keywords: brain imaging, Homonymous visual field deficit, HVFD, stroke rehabilitation
Subjects: Q Science > QP Physiology > QP351 Neurophysiology and neuropsychology
R Medicine > RC Internal medicine > RC 321 Neuroscience. Biological psychiatry. Neuropsychiatry
Faculties/Schools: UK Campuses > Faculty of Science > School of Psychology
Item ID: 71901
Depositing User: Beh, Kuan
Date Deposited: 21 Mar 2024 14:49
Last Modified: 21 Mar 2024 14:49
URI: https://eprints.nottingham.ac.uk/id/eprint/71901

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