Abstract
Chronic misalignment of the eyes (strabismus) during early visual development leads to many well-known functional consequences including loss of visual acuity and stereopsis in addition to a range of other deficits in form and motion processing. Much less is known about the effects of strabismus on the development of brain structure. In the current study, we performed a comprehensive survey of 28 major white matter tracts in 16 patients with amblyopia, comparing their results with 32 age-matched, neurotypical controls. We capitalized on two recent methodological developments to better characterize amblyopia: First, in addition to diffusion-based tractography, we employed a new quantitative T1 mapping procedure that has been shown to be sensitive to myelin in white matter. Second, we analyzed a tract –the Vertical Occipital Fasciculus– that bridges dorsal and ventral visual areas of the occipital lobe. We measured three properties for each tract: fractional anisotropy(FA), mean diffusivity(MD), and T1. A small global effect of amblyopia was reflected in consistently elevated MD and T1 values and decreased FA values in almost all of the tracts. Overall, the most affected property was MD. To assess which tracts were most affected, we rank-ordered the tracts on the basis of their MD effect size. The five most affected tracts showed effect sizes (d’) ranging from 0.74 to 0.58, and were, in decreasing order, the Anterior Frontal Corpus Callosum, Right VOF, Left Inferior Longitudinal Fasciculus (ILF), Left Optic Radiation and Temporal Corpus Callosum. Notably, the VOF is the only long-range tract that lies entirely within the occipital lobe. The ILF connects the occipital and temporal lobes and the two callosal tracts connect frontal and temporal lobe areas. Previous work has suggested that the optic radiation is affected in visual deprivation(Xie et al.,2007).We conclude that strabismic amblyopia has subtle, but widespread effects on white matter properties.
Meeting abstract presented at VSS 2015