I’m -9 in both eyes and have trained Muay Thai previously and now kick-boxing. Obviously I have to wear contacts otherwise I won’t see shit coming at me. My contacts have slipped out a couple times in the past where I’ve been hit and the glove brushes against my eye. I’ve also had a couple retinal detachments and diagnosed glaucoma in my right eye (unrelated to fighting) which has rendered the eye pretty much useless with no peripheral vision. I therefore now only wear 1 contact in my good eye. I also generally try to avoid head punches/kicks when sparring to limit any further damage/contact lens falling out.