The best way to make use of your old glasses is to donate them to charities, (or opticians) that run schemes for sending them to people in developing nations. This helps to give people the chance of better sight when they cant afford to buy the glasses themselves.
The spectacles are collected, dismantled, cleaned and catalogued and sent to countries that can’t make them themselves.
Task forces of opticians are sent abroad to less developed nations and examine eyes while training locals how to do it themselves. Patients are then given a pair of re-used glasses suitable for their prescription.
To donate glasses, either take them into your local Help the Aged store (or other charity shop), or a local opticians (most will collect old spectacles).