Optic Tract Shrinkage Limits Visual Restoration After Occipital Stroke

Background and Purpose: Damage to the adult primary visual cortex (V1) causes vision loss in the contralateral visual hemifield, initiating a process of trans-synaptic retrograde degeneration. The present study examined functional implications of this process, asking if degeneration impacted the amount of visual recovery attainable from visual restoration training in chronic patients, and if restoration training impacted optic tract (OT) shrinkage. Methods: Magnetic resonance imaging was used to measure OT volumes bilaterally in 36 patients with unilateral occipital stroke. From OT volumes, we computed laterality indices (LI), estimating the stroke-induced OT shrinkage in each case. A subset of these chronic patients (n=14, 13 +/- 6 months poststroke) underwent an average of nearly 1 year of daily visual restoration training, which repeatedly stimulated vision in their blind field. The amount of visual field recovery was quantified using Humphrey perimetry, and post training magnetic resonance imaging was used to assess the impact of training on OT shrinkage. Results: OT LI was correlated with time since stroke: it was close to 0 (no measurable OT shrinkage) in subacute participants (<6 months poststroke) while chronic participants (>6 months poststroke) exhibited LI >0, but with significant variability. Visual training did not systematically alter LI, but chronic patients with baseline LI approximate to 0 (no OT shrinkage) exhibited greater visual field recovery than those with LI>0. Conclusions: Unilateral OT shrinkage becomes detectable with magnetic resonance imaging by approximate to 7 months poststroke, albeit with significant interindividual variability. Although visual restoration training did not alter the amount of degeneration already sustained, OT shrinkage appeared to serve as a biomarker of the potential for training-induced visual recovery in chronic cortically blind patients.

Automated summary

Unilateral optic tract (OT) shrinkage can be detected approximately 7 months poststroke with significant interindividual variability. Visual restoration training did not affect the amount of degeneration already sustained, but chronic patients with OT shrinkage close to 0 showed greater visual field recovery compared to those with OT shrinkage above 0.