Designer Hyo-Jong Kim has proposed a pair of eyeglasses that are more like two pairs of eyeglasses!
From the appropriately titled Form Beyond Function:
Prescription lenses are expensive so it’s not often we can afford more than a single pair. Unfortunately that means being tethered to one frame style. Switch Glasses gives you at least two options to fit your mood and lifestyle. The design adds pivots and hinges to the arms and lens of a pair of glasses. By flipping them around, you can take advantage of two different frame colors. Maybe one for work and a funkier one for a night out.
While I don’t agree with his premise about prescription glasses being expensive, I think this is an interesting design. As some of the comments note, the curve of the lens on any pair of glasses prevents you from simply being able to look through the other side of your glasses. The picture above shows the lens being simply turned around. If this is combined with a switch of the left/right side of the glasses, then the curvature issue would be addressed, but the prescription glasses wearer would be required to have the same prescription for each lens (I know I don’t). Regardless, it is certainly an interesting idea!