I'm not an expert but it seems it may be a respiratory disease. In your situation I would isolate those with symptoms, give antibiotics and vitamin supplements / electrolytes in their water and see how they go - that is assuming that they are otherwise acting / eating normally. Oh, and clean their eyes with a mild saline solution or warm water at least once a day. To try to cover additional bases, you could add antibiotic eye drops, such as Neosporin.
This is what i did when i experienced a similar thing in my flock but I'm pretty sure that it is a chronic viral condition, so maybe the antibiotics helped fight off any secondary infections and the vitamins helped boost their immune system but either way, they were all perfectly fine after two weeks and ate and behaved normally throughout.
Good luck and i am sure that more experienced BYC members may be able to offer more comprehensive feedback.
CT