This is still a developing story. Currently, there is no differential diagnosis as to what caused the attack. There is only informed opinion. But in the aftermath of two assassination attempts by rifle, and the Iranian promise to kill Trump, this may become one of the major stories of the campaign. The worst part is that law enforcement does not know precisely who or what caused this, and no one is sure how to prevent its recurrence. This time, President Trump could be the victim.
Most likely it was an infrared laser bought on Amazon.
This seems to be the kind of effect UV light would have. IR would just have a slight heating effect and it would be felt immediately if it was very strong. UV would not be felt and would cause sunburn symptoms.
I thought maybe it was a missing IR filter on one of the stadium lights.
I had read of similar cases in the past