Visual Deficits Associated With Object and Face Images Revealed by Functional MRI in Human Amblyopia

Abstract

Abstract: : Purpose: Amblyopia is a visual developmental disorder characterized by abnormal foveal vision. In normal subjects foveal vision is associated with the representation of faces (Levy et al. 2001). Here we explored possible relationship between the amblyopic deficit and fMRI activation to various object categories. Methods: Fourteen unilateral amblyopic and 3 healthy subjects with normal vision were studied. Each subject signed a consent form approved by the Tel Aviv Sourasky Medical Center. Subjects were scanned on a 1.5 Signa Horizon LX 8.25 GE scanner. BOLD contrast was acquired with gradient-echo echo-planar imaging (EPI) sequence (TR = 3000, TE = 55, flip angle = 90°, field of view 24 X 24 cm2, matrix size 80 X 80). Three fMRI experiments were conducted using red-green filters for monocular stimulation: (1) Retinotopic mapping of the sound eye (2) Presentation of small and large pictures correlating to visual acuity of 6/6 and 6/60 respectively (3) Line drawings of faces and houses of equal size presented to each eye. fMRI data were analyzed with the "BrainVoyager" software package (Brain Innovation, Masstricht, Netherlands) Results: In low order visual areas (e.g. retinotopic) the sound eye's activation was similar to normal subjects. However, in the amblyopic eye, the activation for small pictures was markedly reduced compared to the sound eye, while large pictures' activation was only slightly reduced. In high order visual areas the sound eye's activation was similar to normal subjects while the amblyopic eye showed marked activation reductions that appeared to be more emphasized in the fusiform gyrus compared to the collateral sulcus. Moreover, face images, but not building images show a profoundly reduced activation when presented through the amblyopic eye. Conclusion: Abnormal early visual experience resulting in amblyopia affects in a selective manner the central representation of objects both in low and high order visual cortex regions. Furthermore, our findings reveal the impact of visual experience on the layout of high order face representations.

Keywords: amblyopia • visual development: infancy and childhood • imaging/image analysis: clinical