My first dog would play until she got "heat stroke" (not sure if that's what it was but that's what we called it), and would stumble around like she couldn't see. We would have to take her to the basement, put cold water on her ears, chest, and paws, and turn a fan on her. I don't think she was actually blinded, just disoriented.
EIH is interesting. Not sure its that exactly. It does sound a little scary to have a dog like that. It seems to suggest that eih comes on fast when the dog is doing activity though. Heat intolerance + intense dog.
Could be as simple as heat stroke. I know heat stroke can cause actual blindness (as can other strokes). Who to say exactly where "running hot" progresses to the beginning of heat stroke.