A specialized form of pattern ERG is the multifocal ERG (mfERG) which allows for a different spatial understanding of abnormalities in the central part of the retina. The mfERG is performed with a similar protocol to the PERG, but the light stimulus displays an array of hexagons that flicker between white and black in a pseudo-random sequence^.[9] Depending on the protocol used, multiple ERGs can be produced and associated with regions of the retina^.[9]

mfERG is fairly localized and sensitive, as demonstrated by its ability to detect the difficult-to-find blind spot in the retina^.[9] The spatial aspect of the mfERG is especially useful when diagnosing retinal dysfunction that is localized to specific areas, as is usually the case in conditions like Stargardt’s Disease/fundus flavimaculatus^[10] or Plaquenil toxicity^.[11] The toxic effects of Plaquenil (hydroxychloroquinone) create a distinctive pattern of damage, so mfERGs are recommended for all patients in Plaquenil therapy to detect retinal harm as quickly as possible^.[11]  In disorders that primarily affect the macula and do not cause morphological changes, such as cone-rod dystrophy or early Stargardt dystrophy, mfERG is a highly valuable diagnostic tool^.[12] The mfERG is best for measuring dysfunction of the inner retina and is not sensitive to abnormalities in the ganglion axon^.[9].