To ensure the clarity of vision provided by safety eyewear is acceptable for certain work the refractive properties of the lens must exceed a required level. Lenses can be subdivided into three classes.
Optical class 1 is for work with particularly high vision requirements for permanent use, optical class 2 is for work with average vision requirements, and optical class 3 is for rough work without any special vision requirements (only intended for exceptional cases and not for permanent use).
There are also different optical distortions that give rise to various distortion effects. There are spherical, prismatic, cylindrical and astigmatic distortions. The above-mentioned optical classifications and the associated period of usage depend on the respective distortion effects. As a result, spherical distortions are allocated to optical class 1, prismatic and cylindrical distortions to optical class 2, and astigmatic distortions to optical class 3.