SageGod- that's a tough one. A cage over his eye or protection would help to protect his eye yes. A creature with only one eye would suffer from ridiculous depth perception issues that us bi-clopses have two eyes for. A cage would only "get in the way" and make it harder for him to see- and provide only protection from large things. In order for him to be protected from what he's likely to be facing (mostly tiny arrows) he's going to need a whole plate, which would render him blind. Without glass/a visor I'm having a difficult time coming up with a "proper" solution.