The lenses
The opticians` boxes carry lenses of 25 different dioptres | © Martin Aufmuth

The lenses

The spherical lenses are made of polycarbonate with a hardened surface. The OneDollarGlasses optician has a box with 25 different lens powers from -6.0 to +6.0 diopters in steps of 0.5 diopters. Polycarbonate is much more break-resistant than glass or resin which are commonly used.