I'd bet most of the "blind" hunters that go for this aren't really blind but have odd problems that make their vision unmeasurable instead. I had a friend like that in jr high, without correction his eyes twitched constantly, he could still see OK without glasses but his vision couldn't be measured because of how his eyes behaved. So legally he was blind even though he could see fine, people like him will probably be the ones taking advantage of this law.
In Michigan there are a few totally blind persons ( I mean can see nothing but blackness) that have used the law to hunt deer.
Its not a problem.