Neural degeneration and plasticity following damage to the post-chiasmal visual pathway

Thesis

Hemianopia is a disorder where a patient loses vision in one half of their visual field, following damage to the post-chiasmal visual pathway. If the hemianopia does not spontaneously resolve within the first few months, the prognosis for recovery is poor, with very few patients recovering vision in the affected area of the visual field. The reasons for this are unclear, although it is likely that both degeneration and plasticity in the visual system have an impact on patient outcome. The goal of this research is to investigate the changes that occur in hemianopia, and how these differ for lesions at different locations in the visual pathway and with differing underlying pathologies.

Patients with hemianopia arising from different causes were recruited, including 17 with a hemianopia acquired in adulthood, 9 with congenital hemianopia, and 6 patients with hemianopia due to posterior cortical atrophy (PCA). Structural, functional, and diffusion-weighted MRI data were acquired for each patient, in order to examine changes in the structural and function of the visual pathways. Analyses focused on either atrophy, or plasticity and residual function. Atrophy was assessed in acquired and congenital hemianopia by quantifying transneuronal degeneration in the optic tract, which was present in all patients with long-term lesions. Degeneration was also assessed more generally in PCA, who have substantial loss of white and grey matter in posterior brain regions. Investigation of plasticity and residual function focused on the motion processing area (MT), quantifying the level of functional activity in MT, and assessing whether subcortical pathways from the pulvinar to MT exist in hemianopia. A wide degree of variation existed between patients in the extent to which motion processing was preserved, which had no clear link to lesion location, however was related to the size of the lesion.

Authors: Millington, RS

• Publication date: 2013
• DOI: 10.5287/ora-qxepezjea
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: magnetic resonance imaging; hemianopia; stroke; vision
• Subjects: Medical Sciences; Perception; Stroke