Optic radiation


In neuroanatomy, the optic radiation are axons from the neurons in the lateral geniculate nucleus to the primary visual cortex. The optic radiation receives blood through deep branches of the middle cerebral artery and posterior cerebral artery.
They carry visual information through two divisions to the visual cortex along the calcarine fissure. There is one set of upper and lower divisions on each side of the brain. If a lesion only exists in one unilateral division of the optic radiation, the consequence is called quadrantanopia, which implies that only the respective superior or inferior quadrant of the visual field is affected. If both divisions on one side of the brain are affected, the result is a contralateral homonymous hemianopsia.

Structure

The upper division:
The lower division:

Parts

A distinctive feature of the optic radiations is that they split into two parts on each side:
  • Note: In 2009, an anonymous medical doctor edited the "Optic Radiation" Wikipedia article and added the eponymous name "Baum's loop," referring to the dorsal bundle. Despite the information being unverified, this name subsequently entered scholarly articles and textbooks and persisted until three radiologists discovered the fabrication in 2020.

    Function

The optic radiation contains feedforward tracts that transmit visual information from the geniculate nucleus to the visual cortex, and also feedback tracts from the visual cortex to the neurons in the LGN that project to them. The function of the feedback from the visual cortex back to the LGN is unknown. The optic radiation is activated during working memory tasks. The optic radiations are usually unilateral and commonly vascular in origin. Field defects, therefore, develop abruptly, in contrast to the slow progression of defects associated with tumors.

Clinical significance

Examination

Tracts contained within the optic radiation are examined as part of a cranial nerve examination.