Mapping the Lipid Layer of the Human Tear Film.

To describe a new method to distinguish between normal versus lipid-deficient dry eye using a Tear Film Imager (TFI). Two groups of study subjects, controls versus lipid-deficient dry eye, were tested using the TFI. This instrument provides an accurate measurement of the thickness and spatial distribution of the muco-aqueous and lipid layers of the tear film. The nanometer thickness resolution of the TFI enables the creation of detailed maps of the lipid layer thickness (LLT) across the corneal surface. These maps are captured with a large field of view of 6.5 mm diameter. A LLT map taken at 1 second from a blink end in the controls appears uniform, whereas a nonuniform layer was measured in the lipid-deficient dry eye. Lipid map uniformity can quantify the spatial variation of lipid across the cornea. A case study showed the ability to distinguish between controls [lipid map uniformity (LMU) = 14 nm] and lipid-deficient dry eye (LMU = 125 nm) through characterization of the LLT distribution. High-resolution lateral LLT maps demonstrate the significance of the lipid layer uniformity, which may play an important role in maintaining tear film health. LLT maps and the quantitative LMU could be used to diagnose and treat patients with dry eye.