The reasoning: three inversions and one crossing
- Optical inversion: the superior visual field falls on the inferior retina; the right field on the left hemiretinas.
- Chiasm: nasal fibres (temporal field) cross (~53%); temporal fibres stay.
- Optic tract → LGN (6 layers: 1, 4, 6 contralateral eye; 2, 3, 5 ipsilateral; layers 1–2 magnocellular, 3–6 parvocellular; koniocellular between). Pupillary fibres leave the tract for the pretectum before the LGN; others to superior colliculus (orienting) and SCN (circadian).
- Optic radiations: inferior retinal fibres (superior field) via Meyer loop (temporal lobe) → inferior calcarine bank (lingual gyrus); superior retinal fibres (inferior field) via parietal lobe → superior bank (cuneus).
- V1 (area 17): retinotopic, macula represented at the occipital pole (dual MCA/PCA supply → macular sparing in PCA infarcts); ocular dominance and orientation columns.
- Extrastriate: ventral stream (V4, inferotemporal — "what": form, colour, faces — fusiform face area) and dorsal stream (MT/V5, posterior parietal — "where/how": motion, spatial, visually guided action).