Microstructural differences in visual white matter tracts in people with aniridia.

Aniridia is a panocular disorder characterized chiefly by iris hypoplasia. Most cases result from mutations of the PAX6 gene, which is important in both eye and brain development. In addition to ocular alterations, differences in global brain volume and functional connectivity have been reported in humans with aniridia. Understanding neural alterations in aniridia may require examination of possible differences in white matter structure, as few studies have assessed white matter in this population. The current study utilized diffusion-weighted imaging to assess white matter structure in 11 people with aniridia and 11 healthy comparison participants, matched for sex and age. A map of the local connectome was calculated to compare quantitative anisotropy (QA), an index of white matter tract density, in all white matter voxels, revealing subcomponents of white matter tracts with differing QA between people with aniridia and healthy comparisons. The analysis indicated that QA was lower for people with aniridia in portions of bilateral optic tract [t(20)=-4.23, P=0.001, d=-1.80], bilateral optic radiation [t(20)=-4.06, P=0.001, d=-1.73], forceps major [t(20)=-3.65, P=0.002, d=-1.55], bilateral superior longitudinal fasciculus [left: t(20)=-3.15, P=0.005, d=-1.34; right, t(20)=-4.28, P<0.001, d=-1.83], and right posterior corona radiata [t(20)=-3.19, P=0.006, d=-1.36]. These differences demonstrate that white matter structure is altered in people with aniridia in both visual tracts and associated posterior visual pathways.