I’ll add another pro-Zenni comment. Not just because the glasses themselves are inexpensive (they are though, when I broke my favorite frames it cost $36 to get two replacements), but because it’s a godsend to get glasses you need if your prescription has “expired”. I’m sure there’s good reason for regulating routine vision checkups, but refusing to sell glasses to anyone who can’t get to the appointment isn’t serving anyone.
Yeah, I have never understood whole "prescription" thing in US, here in many (all?) European countries, you just go to eyeglasses shop, they measure your eyes and you get what you want, no prescriptions, nothing. Measuring is usually free if you buy frames from them, if not it cost like 20USD, though you could still go to ophthalmologist to have them measured professionally and it would be free, but you would need to get appointment and there is quite long waiting time and still not sure if they would provide you results for free.
By US logic it's better if people don't have any glasses than bad glasses, strange logic to me.