If you can post a pic that would help. In the meantime, take his temperature and listen to his breathing. A few things come to mind. Could be the start of an upper respiratory infection, or could be entropin (eyelashes curled in and irritating the eye). Treatment is different depending on what you are dealing with.
That is such good news a vet will be seeing him today. You are spot on about not wanting to risk his eyesight. Would you please let us know how is appointment turned out and what the vet says? TY in advance.