Free/Cheap Glasses Information.

All you need to order glasses online is your eye prescription. You can get an eye exam for cheap in many locations. Get a copy of it to take home with you and that's it. Most importantly, make sure that the locations DOES give out your PD number. You might have to pay a few extra bucks. PD number is the distance between your pupils. You will need that measurement for your glasses. Some locations rather NOT give you that number because they know you will go buy glasses online, some are cool and give it to you and some charge an extra fee of like $5.00. 

Once you have your eye exam prescription and PD#, that is it, you can order glasses online easy. 

As you can see by the pictures. The measurements you would want to look for are the Temple Distance, if you have a long or big ol head like I do. You want some long legs on your glasses. The others are lease important but its more of a personal feel. If you have a pair of comfy glasses now, you can measure them and get the measurements you want from it. If its perfect look for one with same numbers, if not, bigger or lower numbers depending on what you want. I personally get a really big comfy pair for the house and a more stylish pair to go out ;)