Positron-emission tomographic study of human amblyopia with use of defined visual stimuli.

PURPOSE The purpose of this study was to use positron emission tomography (PET) to evaluate effects of amblyopia on cerebral blood flow and glucose metabolism in humans viewing defined visual stimuli and to correlate these effects with specific behavioral and electrophysiologic measures of visual function. METHODS One subject with normal vision and five patients with amblyopia were prospectively studied. During monocular viewing of a checkerboard reversal stimulus by each subject, we performed PET imaging of relative cerebral glucose metabolism with use of [18F]fluorodeoxyglucose, PET imaging of relative cerebral blood flow with use of H2(15)O, and visual evoked potentials. Control studies were also performed with use of binocular occlusion and during presentation of stationary and horizontally drifting checkerboards. These data were correlated with letter acuities and contrast sensitivity functions for each eye. RESULTS Although spatial resolution was superior for glucose metabolic imaging, PET readily demonstrated activation of calcarine cortex with use of both metabolic and blood flow tracers. Even in patients with mild amblyopia, functional activation of calcarine cortex was reduced in amblyopic eyes compared with sound eyes to a degree more closely correlated with visual acuity than were visual evoked potential amplitudes to the same stimulus. When responses to drifting versus stationary stimuli were compared, a putative motion processing center was identified in the right temporoparietal region. Activity in this motion center was relatively preserved during viewing of drifting stimuli by the affected eye of an anisometropic amblyopic subject, but was attenuated during viewing of the same stimulus by the affected eye of a strabismic amblyopic subject. CONCLUSIONS PET imaging of blood flow and metabolism can quantitatively evaluate functional deficits resulting from amblyopia in striate as well as extrastriate visual areas. Calcarine cortical function correlates closely with severity of amblyopia, but function in a putative motion processing area may vary according to the type of amblyopia present.