Purpose: To investigate functional changes in primary visual cortex of two glaucoma patients with high resolution (3 Tesla) functional magnetic resonance imaging (fMRI). Methods: Event-related fMRI was applied in this study to verify the hypothesis that the function of primary visual cortex (V1) of glaucoma patients may decrease after severe visual field defect. Two asymmetric glaucoma patients and a normal control subject were enrolled in this study. Blood oxygenation level dependent (BOLD)-fMRI signal was used to infer neuronal activity in visual cortex of the subjects. Results: Standard automated perimetry (SAP) results showed that both patients had severe visual field defects in only one eye. The visual fields of the fellow eyes were normal. The visual fields of the normal control were also normal. In both patients, fMRI signals in V1 area when presented with visual stimuli before the glaucomatous eyes were significantly smaller than those with stimuli before their fellow eyes, P = 0.014 in Case 1 and 0.039 in Case 2, respectively (Mann-Whitney test). They were also significantly lower than average excitatory level of the normal control (P = 0.011 Case 1 vs. control; P = 0.020 Case 2 vs. control, Mann-Whitney test). Conclusion: The event-related fMRI responses in primary visual cortex decreased significantly in glaucoma patients after severe visual field defects.