the invention comprises an apparatus for measuring the relative thickness of the lipid layer component of the precorneal tear film on the surface of an eye after distribution of the lipid layer subsequent to blinking is disclosed . an illuminator directs light to the lipid layer of a patient &# 39 ; s eye . the illuminator 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 . a collector collects and focuses the specularly reflected light 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 , such as projection on to a high resolution video monitor or analysis by or storage in a computer . in order to facilitate ease of measurement , the patient &# 39 ; s head may be positioned on an observation platform when the illuminator directs light to the lipid layer of the patient &# 39 ; s eye .