Tear Break Up Time: How it is checked and what does your eye surgeon see under the microscope?
Tear Break Up Time (TBUT) is an important measure of dry eye, especially in patients who do not clearly show dry eye changes on the cornea or the diagnosis of dry eye is in question.
Patients who have burning, foreign body sensation, chronic tearing, pain, and itching can have an unstable tear film (a cause of dry eye) which causes the tear to evaporate too quickly or may not produce enough tears (aqueous deficiency such as in Sjogren’s syndrome which also is a contributor to dry eye).
How is it done?
In testing for TBUT, sodium fluorescein dye is added to the eye and the tear film is observed under the slit lamp while the patient avoids blinking until tiny dry spots develop. The longer it takes, the more stable the tear film.
A short tear break-up time is a sign of a poor tear film.
>10 seconds is thought to be normal
5 to 10 seconds, marginal dry eye
<5 seconds low (with high likelihood of dry eye symptoms).
An unstable tear film can explain dry eye symptoms in patients who have a normal quantity of tears. Unstable means that the composition of the tears is imbalanced, resulting in tears evaporating too quickly or not adhering properly to the surface of the eye.
Meibomiam gland dysfunction, where not enough lipid is secreted by the meibomian glands to “seal” the aqueous tears and retard evaporation, is a common cause of tear film instability.
This is what we see under the microscope as the tear film evaporates:
This information along with a Tear Osmolarity test, your eye surgeon will be able to determine the cause of your symptoms.