I remember back when I was a paramedic - we had an ophthalmic anesthetic we were allowed to use per protocol - Opthane (I'm not sure if that's the correct spelling of the drug). However, our standing orders were that we NOT administer it until the patient was already IN the ambulance and we were DRIVING down the road to the ER. This was because it is very effective at taking the pain away, so then the patient might say "I don't need an ambulance", walk off, and start rubbing their newly anesthetized eye and causing all kinds of problems that they wouldn't realize because they couldn't feel it.