You could go to a different ER, pretend you just got this one out, that you feel another in your eye, and having horrible migranes. The only way an ER will take you seriously is if you are in horrible pain or danger. They would not want to send you away if you could go blind at their expense later on. Go M-F during regular hours so full lab staff is there. Too bad it has to be a game, but worth a try.
If you want to send it to a lab, I'm sure someone here will have advice for you, I have no experience with labs.