All of them are true about ERG except

Electroretinography (ERG) is the record of changes in the resting potential of the eye induced by a flash of light. Components of normal electroretinogram (ERG) a-wave. It is a negative wave possibly arising from the rods and cones (photoreceptors). b-wave. It is a large positive wave which is generated by Muller's cells, but represents the activity of the bipolar cells . c-wave. It is also a positive wave representing metabolic activity of pigment epithelium (seen only in dark adapted eye). A flash ERG requires a large area of retina to be abnormal for being detectable and thus in macular disorder where only small pa of retina is involved , flash erg doesn't detect it