- Wear sunglasses; UV is very damaging to eyes. I think that glass lenses filter UV but plastic ones don't, though, like everything else I've written here, it's worth checking. I really like these because they fit right over my glasses so I don't have to buy yet one more pair.
- The way you can tell if sunglasses are really polarized is to look at an LCD (like your cellphone screen) through them. If you see wavy lines and rainbows, they're polarized. Otherwise they're just dark. Polarized is better.
Pupil Distance (p.d.) is the distance between your pupils (duh); this should be measured by your optician before when you're ordering your glasses. Some measure it with a ruler; some use that thing that looks like cheap binoculars. It's smaller for close glasses - you bring your eyes closer together when looking at something close.
You can get frames online from:
and probably a lot of other places too. I think it's better to get frames from your optician, since you're probably trying them on there, plus there might be some considerations about your prescription that make some frames a bad idea. But if you really have to cut costs, do it on your frames, not your lenses. I've never found an optician who won't put new lenses in a frame you bring in, though it's sometimes clear that they don't much like it.
When you look at frames, besides the manufacturer, model and color identification (usually on the temples), you'll see a set of numbers like 54-19 or maybe 54-19-140. The first number is the width of where each lens goes ("eye" in picture below), the second is the width between where the lenses go ("bridge" below) and the third, if there, is how long the piece on the side of your head ("temple") is. All the measurements are in millemeters. I don't know why they don't tell you the height, which would be really useful for progressive lens wearers. The above numbers are frequently on the bridge, and very hard for people with presbyopia to read. They also wear off after a few years, so if you care about the measurements, write them down when the frames are new.