Visual Field Defects in Chiasmal Lesions

Classic teaching states that compression of the optic chiasm impacts decussating nasal retinal axons producing a bitemporal hemianopia (BTH). In fact, visual field defects resulting from chiasmal lesions are quite variable1. Junctional scotoma (JXS) is thought to occur with compression of the optic nerve (ON)-chiasm junction where nasal axons from the contralateral eye have been described to make an anterolateral detour forming a structure called Wilbrand's knee2. We hypothesized that the pattern of visual field defect would be predicted by the radiologic appearance of a lesion and its location relative to the optic chiasm.