Uhthoff's symptom that's what happened to me when I had my first flare-up and so far only flare-up with Optic Neurtis I would take a hot bath and then suddenly my right eye got so bad I could hardly see out of it.But about half hour to an hour after I got out of the tub my eyesight returned to normal because my body temp came down to normal. At that time I didn't know I had ON and could't figure it out made a appt with a opthmologist and bingo you got Optic Neurtis and probably MS. That day was the shock of my life.