Duck keeping one eye closed, swollen face?

[TheDaringDucks]

My mallard duck, Yippee, seems to have something up with his face. He's kept one eye mostly closed since yesterday, but it shows no signs of redness or discharge. I've rinsed his eyes with saline last night and it has not improved, but thankfully it hasn't gotten worse either.

He can still open it when he's looking around, but at the moment he just seems to be favoring it a bit. Also, his cheeks also seem a bit swollen to me (he's always had a bit of a blocky head compared to the rest of my flock so I can't say if I'm just imagining the swelling or not). Any thoughts or opinions?

 

[TheDaringDucks]

I've started treating Yippie's eyes with vetericyn, and was able to get a closer look at the one that he keeps closed. It has a slight cloudy film towards the back corner of the eye but is otherwise clear. He is still keeping it closed though after a day and a half of treatment. Any additional treatments anyone would recommend?