The optic radiation, or geniculocalcarine tract, carries visual information from the lateral geniculate nucleus of the thalamus to the primary visual cortex. Its lower fibres, carrying the upper visual field, loop forwards around the temporal horn of the lateral ventricle (Meyer loop) before running back. Its upper fibres pass through the parietal lobe and carry the lower visual field.
| Location | From the lateral geniculate nucleus through the retrolenticular internal capsule, around the lateral ventricle, to the calcarine cortex |
|---|---|
| Parts |
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| Connections | |
| Blood Supply | Middle cerebral artery (deep branches); Posterior cerebral artery; Anterior choroidal artery |
Relays visual signals from the thalamus to the primary visual cortex, preserving the map of the visual field.
Temporal lobe lesions affecting Meyer loop cause a contralateral upper quadrant defect ('pie in the sky'), while parietal lesions cause a lower quadrant defect ('pie on the floor'). Anterior temporal lobectomy risks injury to Meyer loop, and tractography is used to plan surgery. Complete damage causes a homonymous hemianopia.
Loss of the opposite upper visual quadrant after temporal lobe damage to Meyer loop.
Loss of the opposite lower visual quadrant after parietal damage to the upper optic radiation.
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