Is your cham shedding? Maybe your cham has got something in his eye? Lily does that when she sheds - she rubs really hard too. Makes me squirm when she does it! When she sheds I put on a knitted glove and she rubs her eyes on my thumb to get the shed off! Cute but gross at the same time!
My Male Jacksons did that a few days ago!!! I thought maybe parasites behind the eye? He bulged his eye out then rubbed it. Freaked me out. Still not sure.