Optic Tract Lesions

    • Focal damage to the optic tract
    • Causes: neoplasm, aneurysm, vascular malformation, head trauma, neurosurgical procedures, stroke, inflammation
    • Complete homonymous hemianopia
      or incongruous homonymous hemianopia contralateral to the lesion
    • Afferent pupil defect sometimes present in the eye that is on the same side as the homonymous hemianopia
    • Tip: the afferent pupil defect, which is especially common when the hemianopia is profound, occurs because the retinal axon crossing fibers outnumber the retinal axon non-crossing fibers
    • Bowtie (“band,” “butterfly”) optic disc pallor sometimes present in the eye with the afferent pupil defect along with temporal optic disc pallor in the contralateral eye
    • Ophthalmic manifestations may be the only clinical abnormalities
    • Brain imaging often shows the lesion, but it may be subtle
    • Any retrochiasmal lesion can produce complete homonymous hemianopia
    • Tip: if you want to localize a lesion to the optic tract without imaging, you would need either a contralateral incongruous homonymous hemianopia or the following combination: a contralateral complete homonymous hemianopia and a contralateral afferent pupil defect without evidence of an optic neuropathy
    • Perform visual fields on patients whose visual complaints are unexplained by ocular abnormalities
    • If you find a homonymous hemianopia, look for an ipsilateral afferent pupil defect as a means of directing imaging attention to the optic tract
    • Tip: optic tract lesions are often subtle and may escape detection unless you can direct radiologists to that brain region
    • Treatment depends on the cause