Last year my SO and I adopted Pete, a super friendly tabby.
When we got him, he was on meds for a "minor" eye and respiratory infection. We finished the meds left and he was fine.
After some time, we noticed his eyes were bothering him and he was a bit wheezy. We took him to the vet who gave us antibiotics and steroids. He continued to do well.
Flash forward to now and he continues to have horrible problems. We ran out of meds for a bit and he started to just rain dark pus from his eyes. We got meds as soon as we could and he's doing okay, but not great.
The weirdest thing is my SO and I left for Texas leaving him alone with her sister (staying just one day) and her brother (lives upstairs) who gave him his meds. When we got back, his eyes were the best they'd been in a long time. A few days after we returned, all his eye problems came back. The only difference I can think of is while we were gone, her sister basically never left so there were less exposure to outside allergens?
Anyhow, here is a photo of him awhile ago and today. He's currently on steroids, topical antibiotics and lysine gel. I wish I knew what was going on.
Edit: He's been tested for FIV and FEV and was negative.