Abstract
Stroke damage to the primary visual cortex (V1) causes a contralateral loss of vision referred to as cortical blindness (CB), and initiates a process of trans-synaptic retrograde degeneration affecting early visual pathways. In chronic patients (>6 months post-stroke), ipsilesional optic tract (OT) shrinkage can be readily detected by structural magnetic resonance imaging (MRI). It exhibits large inter-individual variability but also predicts the amount of training-induced visual recovery attainable by these patients (Fahrenthold et al., 2021). Recently, preservation of conscious visual discrimination abilities inside perimetrically defined blind fields was observed in a portion of subacute patients (<6 months post-stroke; Saionz et al., 2020). Here, we asked if preserved visual abilities are more prevalent earlier in the subacute period, and if they are correlated with less OT shrinkage. Twenty subacute CB participants 1-5 months post-stroke were analyzed at recruitment as part of an ongoing clinical trial (NCT04798924). Blind-field location and size was obtained from Humphrey automated perimetry. Preservation of fine direction discrimination (>72.5% correct, measurable difference thresholds) was assessed across this region using 5˚ diameter, random dot stimuli. OT integrity was quantified by computing a laterality index (LIOT) from T1 structural MRI scans, thus accounting for individual variance. 7/20 participants exhibited preserved direction discrimination abilities in their blind-field. They were notable in being significantly earlier post-stroke (2.5+/-1.1 months) than participants without preservation (3.9+/-0.8 months; t18=3.17, p=0.005). LIOT values averaged 0.06+/-0.1 across all subacutes, significantly smaller than previously reported for chronic participants (0.4+/-0.4; t46=3.89, p=0.00032). However, LIOT was not significantly different between subacute participants with and without preserved, blind-field, direction discrimination. Thus, in the subacute post-stroke period, preservation of motion discrimination abilities appears most prevalent very early after the lesion, and at least within our current sample, appears uncorrelated with OT shrinkage.