Tear Break Up Time Overview
Why TBUT Matters for Tear Film Assessment
Tear Break Up Time quantifies how long the tear film remains uniform before the first dry spot appears. It is a direct indicator of tear film stability and lipid layer quality, which are critical for clear optics, surface protection, and patient comfort. Abnormally short TBUT values correlate with evaporative dry eye, meibomian gland dysfunction, and inflammatory surface disease. Using TBUT alongside symptom surveys and staining patterns strengthens diagnostic confidence and guides targeted therapy.
Technique and Factors That Influence Accuracy
Instill a minimal amount of fluorescein using a moistened strip or microdrop to avoid reflex tearing, then have the patient blink naturally a few times to spread the dye. Instruct them to hold the eyes open while you observe under cobalt blue illumination and time the interval from the last blink to the first visible break. Keep room airflow low, lighting consistent, and avoid conversation to reduce variability. Repeat at least twice per eye and average the results for better reproducibility.
Normative Values and Clinical Cutoffs
Most protocols consider 10 seconds or longer as normal, 6 to 9 seconds as borderline, and 5 seconds or less as abnormal. Methodology differences, fluorescein volume, and patient cooperation can shift these thresholds slightly, so interpret results within the context of other findings. Record whether invasive (fluorescein) or noninvasive TBUT was used since noninvasive devices often yield higher values. Use the table on this page as a quick chairside reference when staging severity or explaining results to patients.
Common Pitfalls and How to Avoid Them
Excess dye increases reflex tearing and artificially lengthens TBUT, while harsh air conditioning can shorten it. Patients who cannot refrain from blinking or who squeeze lids tightly will skew measurements. Standardize the sequence of tests so TBUT is not performed immediately after anesthetic instillation or vigorous lid manipulation. When results conflict with symptoms, repeat testing at a different visit or add osmolarity and meibography to clarify the picture.
Using TBUT to Direct Treatment Choices
Short TBUT values suggest a need to bolster the lipid layer and control inflammation. Start with preservative free lubricants that contain lipids or polymers to extend stability, and add lid hygiene, warm compresses, or thermal pulsation for meibomian gland dysfunction. Immunomodulators such as cyclosporine or lifitegrast address inflammatory drivers that shorten TBUT, while punctal occlusion helps when aqueous deficiency coexists. Reassess TBUT after major therapeutic changes to document objective improvement.
Documentation, Follow Up, and Communication
Record exact times for each eye, number of trials, testing conditions, and whether fluorescein volume was minimized. Schedule follow up aligned with disease severity and treatment intensity so trends can be tracked rather than relying on single values. Explain results in plain language to patients, emphasizing that the goal is stable comfort rather than a specific number. Consistent documentation supports evidence based adjustments and ensures continuity across providers.