Although postmortem morphological changes in the lateral geniculate nucleus 
(LGN) have been reported in human amblyopia, LGN function during monocular 
viewing by amblyopic eyes has not been documented in humans. We used functional 
magnetic resonance imaging (fMRI) to study monocular visual activation of the 
LGN in a patient with anisometropic amblyopia. Four normal subjects, a patient 
with optic neuritis and a patient with anisometropic amblyopia were studied with 
fMRI at 1.5 T during monocular checkerboard stimulation. Activated areas in the 
LGN and visual cortex were identified after data processing (motion correction 
and spatial normalization) with SPM99. In the 4 normal subjects, comparable 
activation of the LGN and visual cortex was obtained by stimulation of either 
the right or left eye. In the patient with unilateral optic neuritis, activation 
of the LGN and visual cortex was markedly decreased when the affected eye was 
stimulated. Similarly, decreased activation of the LGN as well as the visual 
cortex by the affected eye was demonstrated in the patient with anisometropic 
amblyopia. Our preliminary results suggest that activation of the LGN is 
diminished during monocular viewing by affected eyes in anisometropic amblyopia. 
fMRI appears to be a feasible method to study LGN activity in human amblyopia.