Mine both have occasional runny eyes and the odd sneeze but they are both rescues and were very ill with eye infections when they were first trapped (their mum was feral) and I was warned about it, with them being prone to poorly eyes. I find if I wipe the area around the eye for a couple of days with tepid water with a bit of salt in, it clears up no problem. Anything worse though I'd take them to the vets, my one boy had to have antibiotics after his first vaccine because that made his eyes bad.

I had an old cat that was also very prone to poorly eyes. He was also a rescue but we didnt know his history. Sometimes it would clear up on it's own and sometimes it wouldn't. I think it's def worth a vet visit.

And if it was a pedigree cat and I know their history I would def be off to the vets.