I have a bald faced horse with two blue eyes.
I do three things.
First, I stall her during the heat of the day.
Second, I use 100 spf sun screen on her, everyday, and twice a day when I can.
Third, A full face mask with UV protection, on in the morning, off in the evening.
I haven't had a burn issues sense I started this. She seems to love to sun screen around her eye, and stands quite still while I apply it.
Consistency is the key. Once they're burned it's a different situation.
For we wrestle not against flesh and blood, but against principalities, against powers, against the rulers of the darkness of this world, against spiritual wickedness in high places.