Thirty cases of retrobulbar neuritis (RBN) with varying degrees of myelin loss have been analyzed in terms of loss of chromatic function, loss of spectral flicker detection and reduction in visual acuity. We suggest, from the preliminary results of this study, that there may be two distinct types or stages in RBN. Both stages include moderate to severe impairment or damage to the colour-opponent (and most likely the fine-acuity) system. The second type or stage also involves a conduction block or failure, severely reducing sensitivity to fast flicker, although other luminance functions not involving fast-flicker detection may be spared.