Contact lenses, or therapeutic lenses, are thin lenses that are placed on the surface of the eye. While some wear them for cosmetic reasons, their primary function is to correct and improve vision problems related to refractive errors, act as a protective layer in patients with eye injuries, reduce discomfort

Optical filters carefully transfer light in a specific range of wavelengths or colors while obstructing what remains. These dyed plastic or glass devices are placed in the optical path. They are described by their frequency response, and this identifies how the scale and stage of each frequency component