and make sure that you keep you spares in a good solid case,mine is a old metal one and i keep the glassed wrapped up in one of those micro fiber cloths.
also..when you go for a eye exam you will have a hard time getting the Doc to write the PD on the RX sheet.knowing the PD allows you to order glasses via the web.most Dr's work with a store and the stores have a gizmo to measure the PD but you can do that yourself.before the stores had the gizmo they would just hold a ruler up to you eyes anyway.