Welcome! My name isXXXXX am a 2003 graduate from UC Davis, and currently a Medical Director of a veterinary hospital.
I am sorry to hear about this concern for Gooch.
Very serious because of the severity of the swelling, and not knowing if this is due to an injury, a hypersensitivity reaction (like an insect bite or sting), or if the eye itself is damaged.
Deifinitely, as a precaution, I would give some benadryl antihistamine right now. If you don't have it, don't worry. Just go into any vet, now, for an examination. I would not delay.
Benadryl can be given at a dose of 1mg per pound of body weight. Keep in mind, Benadryl tablets and liquids come in different sizes. So, an approximately 25 pound dog can get a full 25mg tablet or a half of a 50mg tablet. I usually avoid the liquid Benadryl in larger dogs (you would have to give too much of it). You can give Benadryl every 8-12 hours.
If a reaction, a additional steroid shot and possibly some oral steroids to go home will be suggested. Steroids are amazing and very fast for resolving swelling and reactions.
Very sorry to hear what has happened. If there is a concern for the eye, the vet may also recommend a simple eye stain test to ensure there is no trauma or scratch to the surface of the cornea. Eye Stain Test for Ulcers
I hope that information has been helpful.
Please remember to select Reply to Expert, if for any reason you need further clarification, have more questions, or were expecting a different type of answer. Prior to leaving a feedback rating, which I greatly appreciate, my goal is to provide you the best answer possible.