I've never heard of UV light affecting the eye's ability to move. Sounds fishy to me. Many many hundreds of captive chams have done fine under UVB 5.0 lamps. He might be developing a muscle "habit" for some odd reason. If he can see, his eye isn't bothering him, it isn't swollen or discolored, there may not be a problem. I think I'd keep an eye on it (pun intended) to see if anything more substantial develops.