Nothing looks off about the eye - no weeping or any kind of discharge, no obvious white spots on the eye (to my naked eye).
But he keeps scraping above and below his left eye. This is a relatively recent development and I’m concerned that he’s going to actually hurt his eye sooner than later.
It seems a weird time of year for allergies and if it was allergies then I would think it wouldn’t always be the same eye. That seems to be where most ideas end: why is it always the same eye? He moved to a new barn in October and it started not too long after that.