ISO 14997:2017 specifies the physical principles and practical means for the implementation of methods for evaluating surface imperfections. For imperfections specified using the visibility method, two inspection methods are described. The first is visual evaluation of the surface without any comparison standard (IVV). The second is a visibility assessment of a surface imperfection when compared to an artefact of known brightness (ISV). For imperfections specified using the dimensional method, three methods are described. The first is visual evaluation of the surface without any comparison standard (IVD). The second is a dimensional assessment of a surface imperfection when compared to an artefact of known size (ISD). The third is the dimensional measurement of a surface imperfection using magnification and either a comparison artefact of known size or a reticle or ruler (IMD). Instruments exist that allow objective measurement of brightness (digital scatterometry) or size (digital microscopy). While these instruments can be used for evaluation of surface imperfections, they are beyond the scope of this document. ISO 14997:2017 applies to optical surfaces of components or assemblies such as doublets or triplets. ISO 14997:2017 can be applied to optical plastic components; however, attention is drawn to the fact that impact damage to plastic materials often looks very different from that on harder materials as it does not always result in the removal of material but instead can displace material, causing ripples in the surface. Consequently, visual comparisons of scratch and dig damage to plastic with those on glass or crystalline materials can give very different results.