Here in the US...
you go to the optometrist office to get your prescription, then get fitted for glasses (optician?) in the front of the same building. There are lots of frames to choose from, as well as quite a variety of lens types, coatings, etc. But they're expensive - it's easy to spend $500 on a pair of glasses, even AFTER insurance.
Why?
Because the optometrist, the frame-manufacturer (lots of options and brands, but they're all made by the same folks), the lens manufacturer, and even the vision insurance all have the same parent company, Luxottica. LensCrafters, Sunglass Hut, Pearle Vision, Target Optical, EyeMed (rebranded as several vision insurance companies), all are Luxottica companies, which also make the frame brands Chanel, Prada, Giorgio Armani, Burberry, Versace, Dolce, Gabbana, Michael Kors, Coach, Miu Miu, Tory Burch, Ray-Ban, Persol, Oliver Peoples, and Oakley.
If you're in the US, take a look at companies like Zenni. My "$600 after insurance" glasses cost $60 before insurance (then the insurance cheaps out and only covers $45).