I have lesions on my optic nerves, and suffer from the heat visually as well. I have Uhthoffs syndrome (sp?) and when I over heat my vision goes wonky. i dont go blind per se, but I get fuzzy vision. Lets say I was out for a nice brisk walk, and got over heated, it would be like someone smeared vaseline on my glasses. I could tell you that a large golden colored car past me, but couldnt tell you what make it was, nor the license plate of it. I can make out the blur of where the road is, and where the grass is, but cant see sticks or trash that I am about to step on, unless its brightly colored. I am told this is rare for MS patients, and some have it with or without lesions.

Normal everyday heat makes me feel like I have run a marathon. my body wont co operate. I go into slow motion and feel like I gain 100 pounds. I feel wrung out, and if I dont cool off I can get confused, and disoriented.

I will say that being on copaxone (for me) makes these sx worse. When I was off copaxone, I tolerated heat a bit better, and had more energy. I will admit it was beautiful weather during my 2 weeks off, so that is hard to judge.

I find if I push myself past the point of comfort, I can end up with diarrhea, tummy cramps, confusion, severe exhaustion, my legs turn to jelly and feel like they wont hold me up, and I will spend the next 3 days recovering from the event. It will be like I am recovering from a marathon.

btw the humidity is what really throws me. I can deal with some heat, but make it muggy, and I go down like a sack of potatoes.

It varies for each person. Some folks just get wobbly, and tired. Others get the full boat of sx like me.