Which test measures the amount of solutes in the tear film by assessing tear osmolarity?

• A. Schirmer Tear Test (STT)
• B. Tear osmolarity
• C. Interferometry
• D. Tear break-up time

Answer: (B)

Tear osmolarity directly quantifies the solute concentration in the tear film, reflecting how concentrated the tear layer is. This measurement uses a small tear sample and an osmometer to yield a value in milliosmoles per liter, with higher values indicating a greater solute load that is often seen in dry eye due to reduced production, increased evaporation, or inflammation. The other tests assess different aspects: the Schirmer test estimates tear volume rather than solute content, interferometry looks at the tear film’s optical properties and lipid layer, and tear break-up time measures how quickly the tear film becomes unstable after a blink. Therefore, measuring tear osmolarity is the test that specifically assesses solute concentration in the tear film.