I not a vet but could it be a sty or something got under his/her eye lid and got infected....my s-dad had something like that i know human to dog is kinda big but looks like the same thing(my step dad had a peace of steal sliver under his eye and his body made a mass around it till her got it removed kinda gross but its all i got) I hope things turn out ok.
It looks like either a bite of some kind or an infected hair folicle....Try to see if he will let you put a warm rag on it and see if the swelling goes down....Also, maybe try a dose of benedryl if it was from a bite that may help as well....Try not to freak to hard....it does not look like anything to major that can not wait until they can see you!
Well I got Titan into the vet today and she said it could be one of two things. The first thing we are treating is an abcess I have to give him Cephalexin morning and night. She said if that does not work then it could be Meiobeman gland ... something. She said that they have glands all around their eyes and sometimes they do not drain. She said if it is that it will have to be surgically removed. Hopefully these pills will clear it up.