If you wear a simple prescription, it might be possible. However, if you wear progressive lenses, bifocals or trifocals, like I wear, I would want the fitting and placement of the various lenses be done using my head as a guide. When your glasses contain multiple lenses on each side, the placement of them becomes very important. Some people who wear bifocals, want the lens in the middle of the overall lens, I need to have mind move closer to my nose. People with serious eye problems or complicated vision issues should avoid the mail order route.
People seem to do well with mail order contacts. I cannot wear contacts, so I have no personal experience with that type of vision aid.