chiasm
Pronunciation: KY-azm
The anatomical structure where optic nerve fibers partially cross, creating the basis for binocular visual field organization.
Full Definition
The optic chiasm is a crucial anatomical structure located at the base of the brain where fibers from both optic nerves converge and partially decussate. Nasal retinal fibers cross to the opposite side while temporal fibers remain ipsilateral, creating the anatomical basis for the visual field organization seen in the lateral geniculate nuclei and visual cortex. Chiasmal lesions typically produce bitemporal visual field defects, and the precise pattern of field loss can help localize the anatomical site of compression or damage within this structure.
Usage
Usage note: Sometimes written as 'chiasma' in formal anatomical contexts.
In Context
- "MRI revealed a pituitary adenoma compressing the superior aspect of the chiasm." — neuroradiology report
- "The bitemporal hemianopia localizes the lesion to the chiasm rather than the optic tracts." — neuro-ophthalmology consultation