Effects of early blindness on white-matter structures subserving vision

Abstract

Objectives. Sight-restoration attempts after long-term vision loss often had limited success. The outcome of such attempts may depend on the integrity of the anatomical structures subserving vision. The developing visual cortex is known to be experience-dependent. However, the effects of early visual deprivation on white matter structures carrying visual signals remain largely unknown. Here, we use diffusion tensor imaging (DTI) and tractography to compare the occipital-callosal pathway in an early-blind patient with a group of normally-sighted adults. Methods. MM lost one eye and was blinded in the other eye when he was 3 years old. He was 45 years old at testing. DTI data were collected on MM and 16 normally-sighted controls aged 23 to 50 using a 1.5T GE Signa LX scanner. Major pathways in the white-matter, or the fiber tracts, were estimated using the streamline tracking techniques (STT). Occipital-callosal fiber tracts were identified as those connecting the occipital lobes of the 2 hemispheres through the corpus callosum. MM was compared to the controls in the percentage of callosal cross-sectional area occupied in the mid-sagittal plane. Results. MM’s occipital-callosal fiber tracts occupied a significantly smaller percentage of callosal area (3.26%) than the same tracts in normally-sighted controls (9.50 ± 1.84%, mean ± s.d.). There were no significant differences in cross-sectional area of the callosum itself. Conclusions. MM’s occipital-callosal pathway is about half the cross-sectional area of normally sighted adults. Early blindness may reduce the inter-hemispheric connections of the occipital lobes. Such blindness related changes in the occipital-callosal pathways may contribute to the limited success in sight restoration after long-term vision loss.