Optic tract

Last revised by Raymond Chieng on 15 May 2023

The optic tracts are the posterior continuation of the optic nerves after the medial (temporal field) fibers decussate at the optic chiasma.

The optic nerves, optic chiasm, and optic tracts pass through the Circle of Willis in the way that it courses below the anterior cerebral and anterior communicating artery and above the posterior communicating arteries, posterior cerebral arteries, and basilar artery 5.

The optic tracts course posterolaterally through the ambient cistern from the chiasma to the lateral geniculate nucleus of the thalamus. Most axons synapsis with this nucleus and carry visual fibers. A smaller proportion of axons branches off medially from the optic tract to course between the medial and lateral geniculate nuclei and towards the tectal plate to synapsis with the superior colliculus. This small branch, the superior brachium, carry fibers responsible for the light reflex.

The optic tracts are supplied by small branches of the anterior choroidal and posterior communicating arteries whereas small branches of the anterior cerebral artery and the superior hypophyseal artery supply the chiasm and intracranial portion of the optic nerves.

Lesions compressing the tract classically produce the visual field defect of unilateral homonymous hemianopia, where there is loss of both right and left contralateral fields.

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Cases and figures

  • Figure 1: optic tracts
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  • Figure 2: superior brachium (Gray's illustration)
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  • Figure 3: optic nerve and chiasm (Gray's illustration)
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