The tear film is a thin layer approximately 100 nm thick. By irradiating white light on the tear film surface, several interference patterns appear by the difference in the two specular reflection light paths
obtained between the surface and the back of the lipid layer. An advanced optical system designed for the shape of the cornea makes it possible to observe the interference image in a wide area. By the principle of specular reflection, the break-up of the tear film can be observed in a non-invasive manner.