Grey discharge in nostrils and partial blindness?

One of my hens has had thick grey mucus in her nostrils for about a week, and now my rooster also has it as well. The rooster suddenly seems to be partially blind - he can’t see anything within a foot of him but seems to be able to see things that are further away. It looks like he’s struggling to dilate his pupils to focus on closer things, which means he isn’t eating or drinking because he can’t see the food. He is otherwise still acting normal, just tripping over things. But the hen is acting lethargic. Does anyone know what this could be?

It seems like a respiratory infection but I’m trying to narrow down which type it could be so I can get the right antibiotics. My roo is 12 years old and hasn’t had any health problems before, I love him very much and I want to do everything I can to get him healthy again. He does not appear to be suffering or in pain since his demeanor hasn’t changed, so please don’t suggest culling. Thank you to anyone who has advice.