The thing I really hate is that even if you do get a prescription, most optometrists will try to leave out the inter-pupillary distance. This area is mostly governed by state law, not federal, and in my state they're explicitly required to provide that information upon request. I've always had to remind them of this fact before they'll comply. Then, the form on which they provide the prescription - unlike the one they use themselves - usually doesn't even have the space for that information. It ends up being written in the margin, usually unlabeled as one last act of defiance.

It has always seemed rather scummy. That's why I've been buying glasses online for several years, tweaking it a bit based on actual all-day wearing experience each time because a measurement taken at any one time of day is sure to be wrong at another. So it's better as well as cheaper. Just need to find a site that doesn't play the optometrists'game, because some do and some don't.