Interferometric imaging of the full thickness of the precorneal tear film.

A method is described for recording interference images from the full thickness of the precorneal tear film (PCTF). Simultaneous images are recorded by two video cameras. One camera responds to broadband spectral illumination and records interference from the superficial lipid layer of the tear film. The other camera uses narrowband illumination and records interference from both the lipid layer and the full thickness of the PCTF. Thus the full-thickness interference fringes are derived from the difference between, or ratio of, narrowband broadband images. This method has the potential for evaluating the role of both tear film flow and evaporation in tear film thinning and breakup. It therefore may be applied to the analysis of dry eye disease.