If both eyes are red and swollen it may be caused by allergies. If the eye is only red and swollen on one side, it may be due to trauma, accidentally bumping into being touched by a sharp object, playful fights between dogs that accidentally injure the eye can lead to red and swollen eyelids, and in severe cases, corneal ulcers. It can also be caused by something in the eye that the dog keeps scratching, which over time can lead to inflammation, redness, swelling and pain.
