He was neither rolling his eyes backwards nor experiencing episodes of nystagmus (involuntary eyeball movement). Rather, those very "effects" were inherent to his visual anatomy...they were normal and not at all uncommon.
Usually, the eye may have either of two different palpebral openings, i.e., two different shapes:
In the almond-shaped eye, the eyelid conceals the sclera (white membrane) around the iris; the eyelid overlaps with the iris.
In the so-called round eye, a ridge of sclera shows between the eyelid and the iridial (iris) border; a white strip "divides" the eyelid and the iris.
He has eyes of the latter type, so when he maneuvers an eyelid in such a way as he did in that Superbowl clip, the iris gets completely covered and only white matter remains exposed, giving the illusion of an eye rolling (conversely, when he retracts an eyelid, the sclera becomes more prominently visible, giving the illusion of an eye popping).



