The play occurred in the final minute of the first frame, after Johansen's stick came up during a net-front battle with Nathan MacKinnon and slid into the eye hole in Kuemper's mask and caught him directly in the eye.
Kuemper tried to make his way to the Avs bench to get some attention from the trainer but did not make it very far, as he fell just inside the circle in the Avs' zone, with the play being blown dead so he could be attended to. After a few moments, Kuemper was escorted off the ice and directly down to the tunnel.
Obviously, we hope that Kuemper is alright. It was a very unfortunate play and was not at all intentional from Johansen's side of things. For a goaltender to suffer a freak eye injury like that is terribly bad luck. For the time being, Pavel Francouz has entered the game.