We both wear prescription glasses, and we pay out of pocket for vision. If you wear prescription glasses, it doesn't seem likely a vision plan alone would pay off for the buyer. People who don't wear glasses don't buy insurance, so you're in the pool with others who also wear glasses, have exams, etc. just like everyone else. And the premiums would have to be for basic frames and lenses to be at all competitive, so you're going to pay out of pocket for anything more.
Generally insurance is useful when expenses are high, and risk is more random. True for medical, auto and homeowner expenses, much less so for vision or dental for that matter?