Effect of Visual Training on Optic Tract Degeneration after V1 Lesions

Abstract

Damage to the primary visual cortex causes a contralateral visual field defect known as cortical blindness (CB). While some vision can recover spontaneously in the first few months post-insult1, without intervention, a slow, progressive loss of vision characterizes the ensuing months and years2,3. Trans-synaptic retrograde degeneration4–7 may explain this progressive loss, which in humans, manifests by reduced optic tract (OT) size ipsilateral to the lesion8. Given that visual training can reduce the size of visual deficits months to years after occipital stroke9, we asked here if visual training slows or stops this degeneration. As such, we measured optic tract volume in 31 chronic (>6 months post-stroke) cortically blind patients, 17 of whom underwent visual training. About half of the subjects (17/31) exhibited significant OT shrinkage on the side of the lesion, resulting in a positive laterality index (LI), while the remaining 14/31 exhibited similar left and right OT volumes (LI=0). Training-induced visual recovery did not decrease LI, or prevent LI from getting worse in those who had LI=0 pre-training. However, there was a negative correlation between pre-training LI and visual field shrinkage post-training (R2=0.5, p = 0.019). Our results suggest significant heterogeneity in OT shrinkage after V1 stroke, which progresses irrespective of visual training in the chronic period. However, importantly it appears that pre-training LI predicts the magnitude of visual field recovery achievable with visual training in chronic CB, with patients whose LI was 0 before training exhibiting the greatest amount of visual field recovery.