I had VERY good luck with Wal-Mart on my previous pair, about 15 years ago. As a -8, I know I'm hard to fit. Before you decide on the where, you need to have an idea of what might work, especially if you're hard-to-fit.

For instance, I need a substantial, roundish frame that goes all the way around; otherwise, all that plastic in the lenses will be unstable and prone to breakage. For this reason I couldn't get glasses from W-M this time. The optician talked my mom, who was paying, into anti-reflection (VERY bad move) and double thin (I didn't care). However, she also discouraged color change and UV protection, saying neither would work with my Rx.

Oh, BTW, I ended up getting them from my optometrist's office.