Hi XXXXXXXXXXXX~
Is it the area around the eye, or does it seem like the eyeball itself is involved?Do you notice any blood or discharge from the area?
Okay good...I was worried that perhaps your dog had somehow damaged the eye itself, but since that seems fine, then I think I'd try a little Benadryl and see if that helps. This sounds like it could be an allergic reaction or some sort of bug bite and the Benadryl should help with that. The dose is 1-2mg per pound every 12 hours, so if your little dog weighs 25 pounds, he can have 1 or 2 of the 25mg tablets every 12 hours.
If it doesn't look better by morning, or if you notice any discharge, then you should have a vet take a peek at it...just to be safe.
Certified Veterinary Technician
Associates Degree in Veterinary Technology. State and Nationally certified.