just a couple of well meant remarks, as an optometrist and optician (in the old days...)...
@Ringo: if you wear bifocals, they can only mail you another pair if you take exactly the same frames, as the height- placement of the lenses is of primary importance, and is different with every frame.
@Mauricio: Hans Anders is a discount optician with lousy lenses, and can sell the frames at a very nice price because they buy overstocks. Do not try them to get a part replaced. Generally speaking the lenses are a hell of a lot more expensive than the frames, so...
@everybody: there is a huge difference in quality of lenses, and as always, you pay for quality. If you can get anyone of the following brands here, you should be fine. In order of price... Hoya, Nikon, Rodenstock, Zeiss. There is another French brand which is very good, but my old brain now fails me... lol
BelgianK