What is the role of tear breakup time (TBUT) testing in the workup of dry eye disease (keratoconjunctivitis sicca)?

Updated: Dec 12, 2019
  • Author: C Stephen Foster, MD, FACS, FACR, FAAO, FARVO; Chief Editor: Andrew A Dahl, MD, FACS  more...
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Tear breakup time (TBUT) is determined by measuring the interval between instillation of topical fluorescein 0.5% and appearance of the first dry spots on the cornea. Measure it prior to instillation of any anesthetic eye drops. A fluorescein strip is moistened with saline and applied to the inferior cul-de-sac. After several blinks, the tear film is examined using a broad-beam of slit lamp with a blue filter for the appearance of the first dry spots on the cornea. Three consecutive measurements are taken, and the time is averaged to obtain the TBUT. A TBUT of less than 10 seconds is considered abnormal, indicative of tear instability. Several devices can measure the TBUT objectively, including the Oculus Keratograph 5M.

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