Schematic diagram showing the different layers of the tear film spread over the front surface of the eye. The tear film is anchored to the corneal epithelium by long chain mucin (mucous) molecules that attach to the epithelium and extend into the tear film aqueous/mucin layer, which helps to bind the tear film together. On the surface of the tear film is a thin lipid (oily) layer that helps to stop the tears from evaporating.
Schematic diagram showing the different mechanisms involved in the tear film that lead to tear instability and, ultimately, tear film break up.
Close-up view of the front surface of the cornea with sodium fluorescein dye instilled into the tear film. The dark patches in the green tear film are areas where the tear film stability is reduced.
Photomontage of three close-up views of the lower eyelid tear meniscus, showing the reflection (from the meniscus) of an illuminated test object composed of three horizontal lines. The distortion in the reflection produced by the meniscus gives information about the volume of tears in the meniscus. (Courtesy of Dr Stefan Bandlitz)
Greyscale thermal image of the front surface of the eye and the surrounding tissues – cooler temperatures are in darker grey, warmer temperatures in lighter greys. The cornea is cooler than the rest of the eye surface because there is no blood supply to that area.
Tear film collection methods: (L) using a cellulose rod, and (R) using a glass capillary tube