Optic chiasm

Mohamed and Dr Craig Hacking et al.

The optic chiasm or chiasma is the midline structure where the nasal (medial) fibres of the optic nerves decussate to continue posteriorly as the optic tracts. It lies in the chiasmatic cistern and along with the pituitary stalk, is completely encircled by the circle of Willis.

The circle of Willis encircles the pituitary stalk and optic chiasma.

Small branches of the ACA and the superior hypophyseal artery supply the chiasm and intracranial portion of the optic nerves whereas the optic tracts are supplied by small branches of the anterior choroidal and PCom arteries.

Lesions compressing the chiasm classically produce the visual field defect of bitemporal hemianopia, where there is loss of the temporal fields.

Anatomy: Brain
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Article information

rID: 52110
Section: Anatomy
Synonyms or Alternate Spellings:
  • optic chiasma
  • chiasm

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Cases and figures

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    Figure 1: optic nerve and chiasma anatomy
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    Figure 2: midsagittal section
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    Passage of the op...
    Figure 3: optic chiasm
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