Which test assesses tear production by observing the time until the tear film breaks up after a blink?

• A. TBUT
• B. Schirmer test
• C. Phenol red thread test
• D. Tear osmolarity

Answer: (A)

Tear break-up time measures how stable the tear film is on the front surface of the eye. After a blink, you watch the tear film and time how long it takes for a dry spot or break in the film to appear. A longer time means the tear film is more stable, while a short time indicates the tear film is unstable and prone to drying, which is often seen in dry eye. Fluorescein dye under blue light helps visualize the break-up, though noninvasive methods exist.

This test focuses on tear film stability rather than how much tear is produced. The Schirmer test and phenol red thread test both gauge tear production by how much tear wets a paper or thread over a few minutes. Tear osmolarity assesses the salt concentration of tears, reflecting dry eye severity rather than break-up time.