Closing one eye, issue for alarm?

[Kisa]

Hey guys, lately I've been noticing that my White's Tree Frog has been closing only one of his eyes when he sleeps and keeping the other open. It seems a strange question to ask but could there be something wrong with him? I've checked it out thoroughly and it doesn't seem as if he has anything IN his eye and any debris around it he usually wipes away with his hands. Everything else seems to be fine with him, I've even got him to croak very quietly once or twice and he's been spending a lot more time outside of his hut than when I first got him. Just wondering if this eye thing is something I should look into or if it's just a weird mannerism he has.