I used Orbenin ointment in the one and only case I ever had, during the summer it was. I cant remember if I also used an antibiotic, not have my medicine records book to hand now. The ewes eye still looks a bit cloudy, but she can see me (and the food bucket) about 50 yards off, so I think she is not (that) blind anymore....
I certainly have seen midges around recently, and we are much further up north than you are!