The Frames and lenses of tailor-made prescription safety spectacles in accordance with European
standard 166 must feature a permanent mark.

Independent testing institutes carry out certification of the materials at regular intervals.

Frames and lenses must be marked with the manufacturer’s identification and the mechanical strength.
The lenses must also be marked with the optical quality class.

The different methods used to test mechanical strength vary according to the lens material. The test
methods are defined under European Standard EN166.

If the mechanical strength level marked on the lens differs from that on the frame, the lower mechanical
strength applies to the eye protection as a whole