To our knowledge, this is the first case report of bilateral temporal hemianopic defects from a retinal disorder. In this case, the funduscopic examination results were initially normal and the results of mfERG were also thought to be normal, although in retrospect the tracings were contaminated by excessive noise. Subsequently, although repeat mfERG results were abnormal, full-field ERG showed no abnormalities; this was probably because a sufficient proportion of the retina in both eyes had not yet been affected. Full-field ERG assesses overall retinal function. Thus, the poor responses from the abnormal nasal retina that was initially affected and therefore produced what appeared to be bilateral temporal scotomatous field defects were overshadowed by the normal responses from the part of the nasal retina that was still normal as well as the intact temporal retina. This case highlights the potential for retinal disorders to produce visual field defects that mimic those produced by optic nerve or chiasmal lesions, the importance of obtaining appropriate and correctly interpreted electrophysiological tests to assess patients with unexplained visual field defects, and the need to perform serial examinations and repeat testing when the cause of such abnormal visual fields is unclear.