A female presented with loss of vision in both eyes and on examination has normal pupillary responses and normal fundus, Her visually evoked response (VER) examination shows extinguished responses. The most likely diagnosis is

B. i.e. Coical blindness VER assess the functional state of the visual system beyond retinal ganglion cells. Since there is dispropoionately large projection of macular area in the occipital coex, the clinically measured VER is primary a response generated by macula & optic nerve. In any abnormality of macula, optic nerve or the remaining optic pathway (beyond optic nerve), there is increase in latency and decrease in amplitude (extinguished responseQ). The timing of onset of the response (latency) is a more reliable and generally more useful parameter than amplitude. In retrobulbar neuritis latency persists even when vision returns to normal. Delay is therefore an impoant sign of past attack of retrobulbar neuritis.