Optic Radiations

The cells of the M and P layers, along with the K cells, all send axons to primary visual cortex through tracts called the optic radiations. There is a split of axons from the superior retina on each side (representing the lower, inferior part of the visual field) which take a more direct route and the axons from the inferior retina on each side (representing the upper, superior part of the visual field) which take a longer route around the lateral ventricle which includes a feature called Meyer’s loop. Because these axons take a longer route, they are slightly more susceptible to damage, and a visual field defect called “pie in the sky” results. Axons representing a pie-shaped slice of the upper visual field on the contralateral side are damaged; because only ¼ of the visual field is affected on each side (contralateral & superior), this is called a homonymous quadrantanopsia (“same name [location] quarter [of the visual field] not seeing”).