Does that mean blind jews can use this as precedent to eat whatever they like?

Looks like some rabbis might allow some liberal interpretation so I guess the answer is it depends… Flexibility is good.

No, that would be silly. "The Naked Eye" is what normal human eyes can see without aid. There is a lot of grey area there, but microscopic creatures that you can only see with specialized equipment invented in the past 100 years certainly are not visable to the naked eye for any reasonable definition of naked eye.

Within reason, it's nothing, or `betal bshishim` which is equated to one sixtieth. It's void, as a concept, in Hebrew tradition.

It helps if you think about it in terms of historical hardships of the Hebrews. It means if you're hungry and your neighbor cooks for you and there's a tiny bit of non-kosher fat in the soup or something like that, or if you're starving, Yahweh will forgive you because it's such a small amount and you're so hungry it's not right to penalize you for that which you couldn't control. Something that is one sixtieth is colloquially so insignificant that it equates to nil.

This general approach is true within all Jewish traditions. For example, if you get sick on Shabbat you're allowed to drive to the hospital (and doctors are allowed to help you), or if you're ill during Rosh Hashana you don't have to fast. It's a very nice aspect of Judaism: "follow the rules, yes, but don't be stupid about it."