I was very lucky as my horse had an attack of it aged 21, and it was a one off, I was very cautious for a long time afterwards though and probably used a UVA mask for 6 months after the attack.
I lost her at 32, and she didn't have another attack of it.
One of mine had it. She loves rubbing her head, so probably caused it herself.
Needed 2 weeks in a darkened box, then I think another two weeks avoiding daylight i.e. could go out at night. This was iirc because of the atropine which was part of the treatment. Unfortunatley she also got colic, apparently caused by the atropine as well.
This was 2 years ago now, fingers crossed, no recurrence yet! I do keep a fly mask on her in summer now ( although she developed it in the winter).