Ocular surface interferometry (OSI) devices, systems, and methods are disclosed for measuring a tear film layer thickness (TFLT) of the ocular tear film, including lipid layer thickness (LLT) and/or aqueous layer thickness (ALT). The measured TFLT can be used to diagnosis dry eye syndrome (DES). An imaging device can be focused on the lipid layer of the tear film to capture optical wave interference interactions of specularly reflected light from the tear film combined with a background signal(s) in a first image. The imaging device can also be focused on the lipid layer of the tear film to capture a second image containing the background signal(s) present in the first image. The second image can be subtracted from the first image to reduce and/or eliminate the background signal(s) in the first image to produce a resulting image. The resulting image can be processed and analyzed to measure a TFLT.