We present a case in which mfERG and OCT helped to make a diagnosis of an old BRAO in the setting of compound heterozygous MTHFR genotype. A 44-year-old woman presented for evaluation of a 10 month history of persistently cloudy vision OS. She had been worked up previously for MS versus BRAO, and she was on coumadin, folate, and multivitamin at the time of presentation. The patient has a fraternal twin sister who was diagnosed with MS. Dilated fundus examination OS showed subtle inferior optic atrophy with slight narrowing of the inferotemporal retinal artery, and HVF test revealed a superonasal depression OS. mfERG also showed superonasal depression OS. Retinal origin of the chief complaint was further confirmed by OCT, which showed thinning of the NFL in the corresponding region of the retina OS. Coagulopathy evaluation revealed C677T/A1298C compound heterozygous genotype for MTHFR, and plasma homocysteine level after 6 months of folate and multivitamin supplementation was 10 microM (reference range 4-10 microM). The patient was diagnosed with BRAO and maintained on coumadin therapy.