is it in both eyes?
orbenin is great stuff, saved one of mine from pinkeye! Would recommmend if you can to get 2 tubes of ointment and mark them left and right if its both eyes or you could end up going in circles if its an infection.
Have they had a batch of dusty hay? Sounds daft but hay dust can play havoc with the eyes, mine included as we store some of our hay up in the rafters and I get a facefull every time I take some down for the girls