Selective loss of fMRI response to sustained chromatic stimuli In the Parvocellular Layers of the LGN and the Superficial Layer of the SC of Unilateral Adult Amblyopia

Amblyopia or lazy eye is the most common cause of uniocular vision loss in adults, caused by a disruption to early visual development, such as monocular deprivation or abnormal binocular interaction. Histological abnormalities and reduced fMRI response have been found in the human lateral geniculate nucleus (LGN), suggesting functional deficits in the early subcortical visual pathways. As the key subcortical visual nuclei, the laminar responses of the human LGN and superior colliculus (SC) are difficult to detect, thus the subcortical neural mechanisms for amblyopia remain poorly understood. Using high resolution fMRI, we measured BOLD signals from the magno-cellular and parvocellular layers of the LGN, as well as from different depth in the SC of unilateral amblyopia patients and healthy matched controls. Compared to normal controls and the fellow eye, the amblyopia eye showed a selective reduction of fMRI response to sustained chromatic stimuli in the P layers of the LGN, and in the superficial layers of the SC. No selective response loss was found in the M layers of the LGN. These results indicated a selective loss of parvocellular functions in the subcortical visual pathways of adult amblyopia patients.