Optic Radiation Lesions

    • Focal damage to the optic radiations
    • Causes: neoplasm, head trauma, neurosurgical procedures, stroke, inflammation, posterior reversible encephalopathy syndrome (PRES)
    • Complete or incomplete homonymous hemianopia that may be unilateral or bilateral
    • With unilateral incomplete homonymous hemianopias, look for the following localizing features
      • Congruous homonymous hemianopia
      • Superior wedge-shaped (“pie-in-the-sky”) defects indicate a lesion in the anterior temporal lobe (Meyer’s Loop)
      • Superior-dominant defects indicate a lesion in the temporal lobe
      • Inferior-dominant defects indicate a lesion in the parietal lobe
    • Brain MRI usually shows the lesion
    • Complete homonymous hemianopias localize to the retrochiasmal pathway but not to a particular location within that pathway
    • Perform visual fields on patients whose visual complaints are unexplained by ocular abnormalities
    • Look for localizing features on visual fields to differentiate between lesions of Meyer’s loop, posterior temporal lobe, and parietal lobe
    • Use visual field results and accompanying neurologic manifestations to direct imaging attention to the expected location of the lesion
    • Treatment depends on the cause