We are asked all the time if our eye wear is comparable to store XYZ. It depends! Most optometrist that own an optical department sell high quality eye wear at various price points. There are other locations that are only "optical shops" or "vision centers" (they do not have a doctor owner and many are commercially owned) that also sell eye wear at a variety of price points. Both of the previous two options typically have trained optical staff that know about lens options and frame styling as well as how to properly take measurement based off of the eye glass prescription. They also verify and check each pair of glasses that are dispensed to ensure the prescription is correct and that they fit properly on the patient's face.
And yet another option is online. You pick the frame out yourself (but only using a picture, never really ever trying them on). You select your lens options yourself (plastic, polycarbonate, trivex, high index, single vision distance or near, progressive/no-lines, line bifocal, tinting, photochromic/changable tint... the list goes on and on). You enter the prescription data yourself as well as measurements (hoping you did it right...). Pay for them and pray that they are correct when they arrive.
Please click on the link below to find out more about purchasing eye wear online as well as cheap glasses in general.
Here are 10 things to be aware of if you're considering cheap eyeglasses or sunglasses: http://www.allaboutvision.com/eyeglasses/cheap-glasses.htm
Don't get me wrong, all three options in purchasing eye wear (private doctor own optical, commercially owned optical as well as online places) can include "cheap" eye glasses. I seen options that can lure patients into the shop just based on price but not quality! Please be wary of CHEAP glasses. I have seen some acceptable outcomes as well as bad ones. The bottom line is you get what you pay for!!!