Hello, my name isXXXXX and I have over 20 years of experience as a veterinarian.
I'm sorry to hear that Ein's eye is swollen.
Is it his entire eye itself that is swollen?
Or is the pink area around the eye that is swollen?
Below are pictures of animals where one eye itself is more prominent and swollen.
This is usually due to increased intraocular pressure or glaucoma. Some breeds are ore likely to develop glaucoma compared to others and Corgis are a breed more predisposed to developing glaucoma. This is an emergency condition as if the pressure isn't relieved your pup could end up with permanent loss of vision or even a ruptured eye.
If the pink area or conjunctiva is swollen that is called conjunctivitis. It can be due to trauma, an allergic reaction or a bacterial or viral infection.
Below are pictures of dogs with conjunctivitis:
If this looks like conjunctivitis ideally he would see his veterinarian as eyes are delicate structures and can quickly become infected which can lead to loss of vision. I realize that may be difficult to arrange given that it is at night now.
If a veterinary visit isn't possible tonight I can give you a few things to do to make him more comfortable until you can get him seen.
I recommend flushing the tearing eye copiously with sterile saline which you can purchase over the counter at any drug store. This can help remove any foreign body irritants (like a grass awn or pollens) and should make his eye more comfortable.
Then place artificial tears into his eye every hour or two to keep it hydrated and more comfortable.
Then you can also apply a small amount of Polysporin ointment (only use a new tube so that no bacteria are introduced into the eye) 3 to 4 times daily to his eye to help prevent a secondary bacterial infection. Only do this after flushing the eye as if there is a foreign body in it ointment can cause the foreign body to stick in the eye.
All of these things, sterile saline, artificial tears and Polysporin, can be bought over the counter at the drug store.
If he is rubbing his eye place an elizabethan collar so he doesn't cause any secondary damage.
Then have his eye checked by his veterinarian as soon as possible, unless his eye looks normal in the morning, in which case keep him indoors, continue the artificial tears and Polysporin for another 5 to 7 days and watch him closely for a relapse.
Best of luck with your fellow, let me know if you have any further questions.