How long does it take for a foals eyesight to reach its full potential

We want to put a fly mask on our week old foal (colt) and we don't want to impair his vision more or freak him out...

Hi! Foals already have a fairly good eyesight when they are born since sight and of course hearing are their only natural defenses. Though vision in horses is not great to begin with, a foal will have decent sight at a week old. I would personally wait a little bit longer to put a fly mask on if the flies aren't too bad since the colt is still developing response and learning to use his legs and navigate himself.. But if you really find it necessary to apply the mask, it would not present a large probability for damage to put the mask on now.

Best Wishes!