High resolution fMRI of ocular dominance columns within the visual cortex of human amblyopes.

Non-human primate models suggest that amblyopia has a neural basis in the form of a massive reduction in binocular neurons, and in some cases, a shift in ocular dominance of neural activity toward the unaffected eye. To date, the resolution of neuroimaging has been insufficient to investigate the neural basis of ocular dominance in human amblyopia. We used high spatial resolution (0.5 x 0.5 x 3 mm) functional magnetic resonance imaging (fMRI) to obtain maps of ocular dominance within the visual cortex of adult human amblyopes. fMRI maps of ocular dominance were similar in appearance to maps reported in the literature. For each of six adults with early-onset amblyopia, the number of map pixels corresponding to the unaffected eye was greater than the number corresponding to the amblyopic eye. This shift in ocular dominance was not seen for the two adults with later-onset amblyopia, suggesting that a shift in ocular dominance of neural activity occurs only if amblyopia onset is within the critical period of brain development. Our findings demonstrate how fMRI can non-invasively investigate the neural substrates underlying human amblyopia at the cortical column level.