Understanding the anatomy of the optic nerve and visual pathways is important for understanding how lesions in different locations will cause different visual field defects, as illustrated below.
Once leaving the orbit via the optic canal, the optic nerves enter the middle cranial fossa. Here, the two optic nerves unite to form the optic chiasm. Within the chiasm, fibres from the medial side of each retina cross over to form right and left optic tracts. The optic tracts then pass to the lateral geniculate nuclei where they synapse. Secondary neurones subsequently pass from the lateral geniculate nucleus to the visual cortex via optic radiations. Note that when a lesion lies within the optic radiations, the maculae remain unaffected.
Visual field defect examples
Medical student and illustrator