Anyone have experience with a cat that has eye allergies?

I live in AZ and my cat will get occasional eye allergies. It usually isn't an issue and I'll give her some saline but recently she gave herself a mild corneal ulcer. She had to wear the cone of shame and receieve meds. She is better now but as soon as the cone came off she began scratching again. I made sure to trim her nails right away.

The vet gave me some oral predisone (steroid) to give her during bad times, even though i thought an eye version might be better, but I wanted to see if anyone has experience this! I want to be as preventive as possible so she does not injure herself again in the future. Thank you! 

You know, I'm wondering about allergy drops for eyes, the human ones?  Have you asked your Vet about them?  They work great for humans (me, at least) so I wonder if they could work on cats. If you are using saline right now, which we humans use for dry eye...just a thought.

Problem is,though,how do you know until he has already scratched himself, when he has itchy eyes?