What test is used to evaluate tear film stability by timing the breakup of the tear film after a blink?

• A. TBUT testing
• B. Schirmer test
• C. Visual field testing
• D. Intraocular pressure measurement

Answer: (A)

Measuring tear film stability by timing how long the film remains intact after a blink is TBUT testing. In this test, fluorescein dye is placed in the eye, the patient blinks, and the clinician times the interval from the blink to the first sign of tear film breakup on the corneal surface. A longer time means a stable tear film; a short time indicates instability and possible dry eye. Normal values are typically around 10 seconds or more, though exact cutoffs can vary. This test specifically evaluates how well the tear film holds together over time, rather than how much tear volume is produced or other ocular parameters. The Schirmer test measures tear production, visual field testing checks peripheral vision, and intraocular pressure measurement assesses eye pressure.