The sudden inability of a dog to open one eye may be caused by foreign object stimulation, eye injury, eye disease, canine distemper, etc. It needs to be checked at the hospital for further diagnosis. When you find that your dog's eyes suddenly cannot open, you should promptly check whether there are foreign objects or injuries in the dog's eyes, and clean them with saline in time. If there are no foreign objects or injuries, you need to go to the hospital to check whether there are eye diseases such as conjunctivitis. Use anti-inflammatory eye drops to help your dog recover.