What is the lipid layer thickness in healthy humans compared with humans with EDED?

• A. 100 nm in healthy humans; 83.9 nm in humans with EDED
• B. 83.9 nm in healthy humans; 100 nm in EDED
• C. 60 nm; 40 nm
• D. 120 nm; 95 nm

Answer: (A)

The lipid layer is the outermost part of the tear film and is mainly produced by the meibomian glands. Its thickness helps minimize evaporation of the aqueous layer. In healthy eyes, this lipid layer is relatively robust, around 100 nanometers, providing good protection against tear evaporation. In evaporative dry eye disease (EDED), meibomian gland dysfunction reduces lipid secretion, thinning the lipid layer to about 83.9 nanometers. This thinner layer evaporates more quickly, contributing to dry eye symptoms.

So the pattern shown is healthy eyes with a thicker lipid layer and eyes with EDED having a thinner layer. The other numeric pairings either invert the relationship or fall outside typical measured ranges for LLT.