When you update your prescription or you want to change your glasses style, don't throw away your old eyeglasses. You can donate them to the organizations recycling the glasses. They will send these glasses to people who cannot afford the eyewear.
You can donate them to your local organizations.

US:
ONLINE OPTIONS FOR MAIL-IN DONATIONS
Respectacle: This not-for-profit also accepts donated glasses by mail, which are then distributed to under-served communities. They also have some locations around the United States. 
Address:
ReSpectacle
529 2nd Street, Suite 100
Hudson, WI 54016

NATIONWIDE LOCATIONS THAT ACCEPT EYEGLASSES
Goodwill: Goodwill partners with other nonprofits to provide low-income people with used eyeglasses. 
Find your local Goodwill here.