A sudden swollen eye in a dog may be caused by eye inflammation due to eye disease, eye injury, or mosquito bites. Conjunctivitis and keratitis are common eye diseases in dogs. If you find that your dog's eyes are red and swollen, you need to clean the eyes with normal saline to have an anti-inflammatory and sterilizing effect, and then instill anti-inflammatory eye drops. If the situation In more serious cases, you need to go to the hospital for examination in time to avoid worsening of the condition.