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Samantha I Cunningham, James D Weiland, Natasha Lepore, Yaqiong Chai, Bosco S Tjan; Tract-specific analysis of visual stream structural connectivity in late-blind patients with retinitis pigmentosa. Invest. Ophthalmol. Vis. Sci. 2014;55(13):5850.
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Neuroimaging studies suggest that vision deprivation in humans leads to functional changes in the visual cortex and visual integration sites, specifically in visual association areas of the parietal lobe and along both ventral and dorsal visual streams. We used tract-specific analyses (Zhang et al., 2010) to determine if vision loss also leads to localized changes in visual stream white matter fiber tracks in late-blind individuals with retinitis pigmentosa (RP), an inherited degenerative photoreceptor disease that progressively diminishes vision.
Seven RP and 2 sighted subjects underwent a series of DTI and whole-brain resting-state scans. Diffusion tensor images for all subjects were registered to a common atlas that includes medial-representations of 4 white matter tracts: the corpus callosum (CC), inferior fronto-occipital tracts (IFO), inferior longitudinal tracts (ILF), and superior longitudinal tracts (SLF), all of which have connections in the occipital lobe. Tract-specific regression analyses were conducted to identify significant relationships between subjects’ visual function (i.e. visual acuity and fractional preserved visual field) and mean radial diffusivity (RD), apparent diffusion coefficient (ADC), axial diffusivity (AD), and maximum fractional anisotropy (FA) along the 4 tracts. We further defined the functional connectivity along a tract as the correlation (r) between the time courses of 2 ROIs (one at each end of a tract) after regressing out head-motion parameters.
Regression analyses revealed no significant relationship between visual function and mean RD, ADC, AD, or maximum FA values along the 4 white matter tracts examined (FWER corrected, min. p = 0.151). Resting-state results revealed a trending correlation between the functional connectivity of SLF and subjects’ visual field (r = -0.749, FWER p = 0.078).
These results suggest that vision loss in late blind patients does not lead to obvious changes in fiber tract integrity detectable with a small group of subjects. If sustained with data from a larger study, this finding will reaffirm the viability of sight-restoration treatments on individuals with RP, as the underlying anatomical connectivity between the visual system and other parts of the brain is unaffected by lack of visual input.
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