Do humans with evaporative dry eye disease (EDED) tend to have increased or decreased tear osmolarity compared with healthy individuals?

• A. Increased
• B. Decreased
• C. Normal
• D. Unchanged

Answer: (A)

Tear film osmolarity is a measure of how concentrated the tears are. In evaporative dry eye, excessive evaporation of the tear film due to meibomian gland dysfunction or a thin lipid layer concentrates the remaining tears. This hyperosmolar environment stresses the ocular surface, driving inflammation and epithelial damage, which is a key feature of the disease.

Because the evaporation removes water but not solutes at the same rate, osmolarity increases compared with healthy individuals. A decreased or unchanged osmolarity would not fit the mechanism of evaporative loss, since the tear film would need to be more dilute or exactly the same, which is not observed in this condition.