Prosopagnosia, also known as face blindness, is a cognitive disorder where sufferer can't recognise faces .. Even those most familiar to them, like their children, their spouses, their parents, and even their own. It's thought to be the result of abnormalities, damages or impairment in the right Fusiform Gyrus, a fold in brain that co-ordinate the neural systems that control facial perception and memory.
Yes.. even I thought so.. but then I think that's how patient would have explained! Normal people can't imagine what it's looks like suffering from it!