They go by many names but this is an easy project if you have a little bit of time. The idea is simple, make a strap to hold your glasses when not wearing them or making it tight on your head so as not to fall off.
Step 1: Items needed:
White silicone tubing - 3/16in inner diameter, 5/16in outer diameter, 1/16in wall.
Paracord - 36 inches
Lighter - (or other source of fire to melt ends)
Rounded cord lock
Note: Hobby shops also have loops that are used for holding glasses. The loops are actually one loop with a crossbar to make a figure 8. This can be used in a configuration instead of the tubing.