What does the abbreviation BUT refer to on a patient's chart regarding tear film?

The abbreviation BUT, when found on a patient’s chart in the context of tear film, refers to "Break Up Time." This is a critical measurement used in ophthalmology to assess the stability of the tear film on the ocular surface.

Break Up Time indicates how long it takes for dry spots to appear on the cornea after a patient has blinked, reflecting the integrity and quality of the tear film. A shorter BUT can suggest that the tear film is unstable, which could lead to dry eye symptoms. This measurement is essential for diagnosing and managing conditions related to dry eyes and other tear film deficiencies.

The other options, while they may sounds plausible, do not correspond to recognized ophthalmic terminology or concepts commonly used in assessing tear film health.