My 12 year old neutered male cat has had slightly swollen eyes with a clear discharge for the last week off and on. Just when I think he's better, he gets it again. He's also been sneezing off and on. He's using the litterbox normally, eating and drinking also.No diet changes. His 'third eyelid' also shows at times.He is let out of the house daily, with supervision. Could it be a virus? Should I be cleaning his eyes with something? Any suggestions would be appreciated. His housemate is fine.