A method for measuring the relative thickness of the lipid layer component of the precorneal tear film on the surface of an eye. Light is directed to the lipid layer of a patients eye with an illuminator that is a broad spectrum light source covering the visible region and is a lambertion light emitter such that the light source is specularly reflected from the lipid layer and undergoes constructive and destructive interference in the lipid layer. The specularly reflected light is collected and focused using a collector such that the interference patterns on the tear film lipid layer are observable. The collector also produces an output signal representative of the specularly reflected light which is suitable for further analysis.
