In amblyopia, the number of visual cortical neurons are reduced and abnormal or absent sensitivity to retinal light stimulation of the amblyopic eye is demonstrated. Ten amblyopic patients were studied to evaluate the response of the visual cortex to visual stimulation. Methods: All patients with unilateral amblyopia received 500-550 MBq (TC)-T-99m-HMPAO during Visual stimulation. Strobe light flashing was used as the stimulus for five patients and a checkerboard pattern reversal was used in the other five patients, closing one eye. For both groups a 2-Hz frequency was used. One week later, the same procedure was repeated with the opposite eye closed. SPECT images were reconstructed with prefiltering techniques and sliced along the orbitomeatal line. Results: For all patients, the amblyopic eye demonstrated less radioactivity in the visual cortex than in the normal eye. The mean cerebral-to-cerebellar ratios were 0.95 +/- 0.05 and 1.09 +/- 0.07 for amblyopic and normal eyes, respectively (p < 0.0001). Conclusion: Visual cortex response of the amblyopic eye to light stimulation was severely reduced when compared to the normal eye.