I've had Iritis, AKA UVeitis. It's an autoimmune disorder where out-of-nowhere your body start attacking your iris as though it were a foreign invader. The first time I had I thought it was pinkeye as my eye was bright red and I figured it would just go away after a few days. Well, a few days passed and I woke up one morning and went to the mirror to wash my face and my pupil had become vertically elongated, like a cat's eye and white blood cells had filled my eye so much that a stream of white was flowing down the bottom of my pupil to the bottom of my iris. I nearly went blind in that eye, save for a panicked trip to the eye doctor and a very aggressive course of steroid eye drops. That was fun.