Due to poor mechanical design, the spring hinge of my glasses broke twice. Once while still under warranty, and it got exchanged for free. Then once again now, but the warranty is over. Being self-darkening prescription glasses, they were not cheap. Gosh...

So I decided to repair them using 1mm thick steel string (*) to form a hinge and temple in one single piece.

This method may not apply to any glasses. It depends on how the hinge is made.

(*) that is used in RC models to transmit the force from servos to controls.

Step 1: Make a New Hinge

With pliers, make a loop with the steel string. You can use a small screwdriver to roll the string around.
The internal diameter must correspond to the original hinge screw.
Cut out the excess string, and hammer the loop flat.
Adjust the loop so that it turns smoothly into the hinge, with proper angular limitation. This is the only tricky part.
Assemble using the original hinge screw.

Step 2: Shape the Temple Tip

Determine the proper temple length, and bend the string to form the tip. Cut out excess length.

This repair was so much more stable than the original design that I decided to also replace the other, non-broken temple.

Step 3: Done

Now the glasses can be used again.
For more comfort the tips could be coated with Sugru or similar.

Final note
I know, this covers the functional and structural aspects, and does not give a very fashionable look.
But wait, I have added some definitive coolness in my next Instructable!