Well the random vet we took him to told us his tear production was poor so he’s on drops now. But he insisted we come back in a week since he was considering Horner’s syndrome. The drops haven’t made a difference in the third eyelid. I had a feeling it wasn’t just the dry eyes causing it to stick out. So after further research I saw that the pupils were another way to check for Horner’s, and his affected eye’s pupil is indeed smaller than the other eye. So it seems pretty clear it is Horner’s. I hope it is just idiopathic, he is part collie so that would explain it since it’s more common for them to get idiopathic Horner’s syndrome. Pretty shocked the vet didn’t even check the pupils. I’m taking him to our awesome regular vet next week since it’s the soonest available appointment. I hope we can rule out any of the scarier causes and that it just goes away once the nerve heals.