What does the BUT (break up time) test assess?

The BUT, or Break-up Time test, is specifically designed to assess tear quality. This test measures the stability of the tear film on the surface of the eye. During the test, a small amount of fluorescein dye is introduced into the eye, and the time it takes for dry spots to appear on the cornea after a blink is recorded. A shorter BUT indicates an unstable tear film and suggests poor tear quality, which can lead to dry eye symptoms and other ocular surface issues.

Other options relate to different aspects of tear or eye function. While assessing tear quantity would focus on the volume of tears produced, and lid function would involve the effectiveness of blinking, corneal integrity pertains to the health and structure of the cornea itself. The BUT specifically targets the quality of the tear film, which is crucial for maintaining comfort and protecting the ocular surface.