In ADDE, which description best reflects the effect on the tear film lipid layer?

• A. Increased aqueous layer prevents adequate spreading of the lipid layer
• B. Decreased aqueous layer prevents adequate spreading of the lipid layer
• C. Decreased lipid layer thickness spreads
• D. Tear film evaporation reduces

Answer: (B)

In aqueous-deficient dry eye the tear volume is reduced, so there is less aqueous surface for the lipid layer to spread over. The lipid layer sits on top of the aqueous layer and relies on that surface to spread evenly. When the aqueous layer is diminished, the lipid layer cannot distribute adequately, becoming uneven or patchy, which compromises the tear film's stability and promotes faster tear breakup and evaporation. This is why the statement describing decreased aqueous layer preventing adequate spreading of the lipid layer best fits the effect on the lipid layer in ADDE. Increasing the aqueous layer would improve spreading, decreasing lipid layer thickness isn’t the primary description of this mechanism, and tear film evaporation is a consequence rather than a direct description of how the lipid layer spreads.