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POD10 Demonstration of optic tract atrophy in hemianopia by magnetic resonance imaging: confirmation of retrograde trans-synaptic degeneration in the human visual pathway
  1. G Plant,
  2. J Barbur,
  3. P Jindahra,
  4. H Bridge
  1. National Hospital for Neurology and Neurosurgery, London, UK
  1. Correspondence to gordon{at}plant.globalnet.co.uk

Abstract

Degeneration of retinal ganglion cells in acquired hemianopia (HH) has been shown using optical coherence tomography. We hypothesise that change in the ipsilesional optic tract (OT) should be found using MR imaging. Three cases of HH for >10 years, two for <2 years and 10 controls were recruited. Images were acquired on a 3-T Siemens TIM Trio. The images were re-oriented to cut along the axis of the OT and perpendicular to it. Two masks were then drawn: the cross-sectional area at the third slice posterior to the chiasm and the OT volume measured across all slices in the axial plane in which the OT was both visible and distinct from adjacent white matter. To obtain objective boundaries, a threshold was applied such that voxels not corresponding to white matter were excluded. The number of voxels in each mask was then measured at a range of intensity thresholds. Increasing the intensity threshold means that the tissue contributing to the mask will contain a higher proportion of white matter and the size of the mask will be reduced. The results have been expressed as the ratio (left OT):(right OT). In the three longstanding cases both the volumes (mean ratios: 0.48, 0.5, 0.53) and the cross-sectional areas (0.41, 0.48, 0.6) of the ipsilesional OT were decreased across all thresholds. The two patients with more recent damage were similar to controls. Using standard MR images we have confirmed transsynaptic retrograde degeneration in the ipsilesional OT in longstanding HH.

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