Kelly Chang¹ (), John Pyles¹, Ariel Rokem¹, Ione Fine¹, Woon Ju Park²; ¹University of Washington, ²Georgia Institute of Technology

Early visual deprivation alters the structural development of the visual system. Prior work found decreases in white matter diffusion fractional anisotropy (FA) in the visual pathways of congenitally blind individuals (Reislev et al., 2016; Schoth et al., 2006; Shimony et al., 2006; Shu et al., 2009). Decreases in FA are often interpreted as evidence of reduced myelination in visual pathways following early blindness, but they may also reflect changes in white matter spatial configuration (e.g., axon tortuosity). To distinguish diffusivity-driven changes from myelin-sensitive tissue properties, we collected multi-shell diffusion MRI and quantitative R1 maps (multiparameter mapping sequences) from 8 early blind individuals (3 females, 55.6 ± 15.6 SD y.o.) and 8 sighted controls (4 females, 53.9 ± 13.2 SD y.o.). Vision-related white matter tracts, including the optic radiations (OR), vertical occipital fasciculus (VOF), and forceps major, were segmented using pyAFQ (Kruper et al., 2021, 2025), along with two non-visual comparison tracts (acoustic radiations and motor corpus callosum). Diffusion metrics from the diffusion kurtosis model, such as FA, kurtosis FA (KFA), mean diffusivity (MD), and axial diffusivity (AD), were sampled at 100 equidistant nodes along each tract. Quantitative R1 maps were sampled along the same tract profiles to assess myelin-sensitive tissue properties. Early blind participants exhibited lower FA, KFA, and AD than sighted participants across all vision-related tracts, except the left VOF. In contrast, R1 values were not significantly different across groups in these tracts. No significant group differences were observed in non-visual tracts in either diffusion or R1 values. The combined diffusion and quantitative MRI results suggest that early blindness is associated with reduced axonal microstructural complexity rather than large-scale reductions in myelination along visual white matter tracts. The findings challenge the common assumption that reductions in diffusivity are associated with decreased white matter myelination following early blindness.

Acknowledgements: NEI R00 EY034546 and Georgia Tech Smithgall-Watts Early Career Award to WP; NEI R01EY014645 to IF.