I usually initially treat any possible eye problem on pretty much anything with a rinse of contact solution/saline. No matter what the problem is that should at least not do any harm whereas using certain eye treatments could make other conditions worse. It's probably a twice monthly event around here that someone's eye is getting irrigated and clears up most minor issues. If that doesn't lead to it improving after a day or 2 we visit the vet or just try some terramycin ointment depending if we are talking about a more expendable animal or one of my several thousand dollar horses or dogs. Eye problems are one thing where we never just wait and see. They need treated swiftly or they can go from very mild to permanent damage and in some cases ongoing health issues within days. We had a guinea pig that eventually came down to surgery or PTS because of a nick on his eye that we missed for the first 48hrs after a fight with another boar. We were concentrating on treating the shoulder wound on the opposite side and failed to notice the eye problem until it was glossed over and swollen. By then it was too late and the damage led to repeat infections for the rest of his life.
Any ideas what it might be? It wasn't there yesterday when I checked them and his/her eyes have looked great. 
