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Meghan J Marino, Alex Yuan, Stephen Jones, Katherine A Koenig, Jian Lin, Wanyong Shin, Aleksandra V Rachitskaya, Mark Lowe; Structural and Functional Connectivity of the Optic Radiation in Ultra Low Vision Patients. Invest. Ophthalmol. Vis. Sci. 2018;59(9):4665.
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© ARVO (1962-2015); The Authors (2016-present)
Prior diffusion tensor imaging studies in blind populations have shown decreases in white matter anisotropy in optic radiation compared to sighted controls. Functional connectivity studies have shown alterations in the cerebral connectivity of many visual regions associated with blindness. In this observational clinical study, we examine the relationship of structural and functional connectivity of lateral geniculate nucleus (LGN) to primary visual cortex (V1) pathway, the optic radiation, in Argus II patient candidates.
Two patients (male, 68 and 76 years) with ultra-low vision (>2.9LogMar), equivalent to bare light perception, were scanned to assess functional and structural connectivity in the brain. One was scanned in a 3T MRI scanner with a 32 channel head coil, and the other was scanned in a 7T scanner with a 32 channel head coil (Nova, Inc). Resting state functional MRI (rsfMRI) scans were corrected for motion and physiologic noise. Nine-voxel in-plane seeds were placed bilaterally in the LGN and V1. Within each hemisphere, the timeseries from the two seeds were correlated. The normalized correlation was averaged across hemispheres and taken as a measure of the strength of rsfMRI in the LGN-V1 pathway. The seed regions defined above were used as seed (LGN) and target (V1) regions for probabilistic fiber tracking. Pathway-dependent radial diffusivity was calculated using the track density map, scalar diffusion values, and a white matter mask and averaged across left and right hemispheres.
Optic radiation radial diffusivity for patient 1 was 0.663x10 mm /s and was 0.549x10 mm /s in patient 2. Functional connectivity for patient 1 was r=0.34, and for patient 2 was r=0.49. Patient 1 has optic radiation radial diffusivity that likely represents impaired white matter, based on prior reports of diffusivity for that pathway. This patient also shows reduced functional connectivity between LGN and V1.
We present here, for the first time, a combined measurement of functional and structural connectivity in the optic radiation in ultra-low vision patients. The results reflect the general finding that structural and functional connectivity are related in directly connected pathways. The degree to which structural and functional connectivity are preserved in long-term ultra-low vision and blind patients may impact their response to potential treatments to restore vision.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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