Our litters of farm cats keep getting this, and the vet will not give me any ointment unless he sees them - and he charged £25 last time - plus the ointment cost.
My friend is into herbal remedies for animals, and told me to go to Boots or any health food shop, and get some crab apple (suppose we could make our own with all the apples growing wild near us just now!) Anyway, a few drops in some warm water, and dabbed on with a tissue twice a day, and also add a little crab apple to the cats water or food just a couple of drops - and within a few days, the kittens were as good as new.
I now use crab apple for all sorts of ailments in my animals - such a shame the bottle is so small. Costs about £6