You should check out Opternative. They do eye exams using your computer, though I'm not sure if they're licensed in every state.
Believe it or not, it used to be illegal (in certain US states) to purchase reading glasses 'over the counter'.
That's right, reading glasses were by prescription only.
I have my vision checked in the contact store itself (for free) if I need it and then a proper eye exam during my annual physical check up (which is fully subsidized by my employer - a common practice, albeit at varying levels of support).