Abstract
Introduction Albinism is an inherited condition caused by mutations in genes involved in melanin synthesis. The lack of melanin results in ophthalmic deficits such as reduced visual acuity and misrouting at the optic chiasm (OC). Structural MRI has revealed narrower OCs and smaller lateral geniculate nucleus (LGN) (McKetton et al., 2014). The number of LGN relay neurons has been linked to LGN volume, suggesting a correlation between LGN size and the number of tracts traveling through the optic radiation (OR) to the primary visual cortex (V1) (Yucel et al., 2000). Using diffusion data and both deterministic and probabilistic tractography, we studied differences in the primary visual pathway between albinism and controls. The medial geniculate nucleus (MGN), an auditory nucleus adjacent to the LGN, was investigated to observe potential compensatory alteration in morphology and connectivity. Methods Patients and controls were scanned using a Siemens Trio 3T MRI scanner and 32-channel head coil. LGN regions of interest (ROIs) were created from multiple registered and averaged proton density weighted images. A T1-weighted 3D-MPRAGE sequence with 1 mm3 isotropic voxel size was used to generate high-resolution images for V1 segmentation. Diffusion tensor imaging (DTI) scans were acquired with 64 diffusion directions. Both deterministic and probabilistic tracking methods were run and compared, with LGN as the seed mask and V1 as the target mask in diffusion space. Mean fractional anisotropy and diffusivity maps of visual structures were compared in both groups. Results Our results reveal areas of significantly reduced white matter integrity within visual structures including the OC and OR in patients with albinism compared to controls. We also observe reduced MGN volumes in albinism compared to controls. Conclusions We have demonstrated altered structural development in visual pathways and possible sensory cross-modal interactions using structural and diffusion MRI.
Meeting abstract presented at VSS 2016