It's almost certainly a sinus infection I think.  I don't know anything about geese but we went through this with our peacock, and people who know way more than me told me that is probablywhat it was.  I would guess geese are similar.  We treated our peacock with Cipro/ Baytril and ideally we should have been able to catch him and treat his eye further with antibiotic eye  drops and he might need to have the lump lanced.  I never was able to do this with the peacock.  He did improve hugely just with the Baytril.  I can't say he's 100 % better but definitely at least 98%. We are in a wait and see mode at this point with him.  If your gander is at the point where you can handle him, try some antibiotic gel, Triple Antibiiotic ointment, on his eye, if you can't get anything else. Use human eyewash first or saline solution, to cleanse the eye, and then applyl the gel.  You need to do this a few times a day.  Oh, also, some feed stores sell this antibiotic air gun type thing, I haven't seen it, but read about it, you can puff the eye with the stuff without actually touching the eye. The best solution for the eye is polydex or cipro eye drops, but you have to order those.  At least we do here.
Use the gel in addition to the injections, if that's all you can get hold of.