What Is Tear Breakup Time and Why Is It Important?

Tear Breakup Time (TBUT) is a diagnostic test that measures the stability of the tear film on your eye’s surface. This procedure evaluates how quickly this layer of moisture breaks down after a blink, providing information about tear quality. Stable tears are important for maintaining comfort, clear vision, and eye protection, and an unstable tear film is a common cause of ocular discomfort.

Understanding the Tear Film

The tear film is a complex fluid that covers the cornea and conjunctiva. It consists of three distinct layers that work together to protect and nourish the eye’s surface. The innermost mucin layer is produced by goblet cells and acts as an anchor, helping the tear film adhere evenly to the cornea.

The middle aqueous layer makes up the bulk of the tear film and is mostly water, produced by the lacrimal glands. This layer hydrates the cornea, washes away debris, and provides antimicrobial proteins. The outermost layer is the lipid, or oily, layer, secreted by the meibomian glands in the eyelids. This oily layer covers the aqueous layer to prevent it from evaporating too quickly.

The Measurement Process

The most common method for measuring TBUT involves a practitioner applying a small amount of fluorescein dye onto the eye’s surface, often with a small paper strip. After the dye is applied, you will blink a few times to evenly spread the tear film. You will then rest your chin on a slit lamp, a type of microscope that allows for detailed examination of the eye.

The practitioner will use a cobalt blue light filter, which causes the fluorescein-stained tear film to become clearly visible. You will be instructed to stare straight ahead and avoid blinking. The practitioner then measures the seconds that pass between your last blink and the appearance of the first dry spot, which indicates the tear film has broken up. Some clinics use non-invasive methods that detect these breaks without dye.

What the Results Indicate

A result of 10 seconds or longer is considered normal, indicating that the tear film is stable and provides adequate protection. A TBUT of less than 10 seconds is indicative of tear film instability. A time under five seconds is a strong indicator of a problem, often leading to a diagnosis of evaporative dry eye disease.

This condition occurs when tears evaporate from the eye’s surface faster than they should. The primary cause of this rapid evaporation is frequently Meibomian Gland Dysfunction (MGD). MGD is a condition where the glands that produce the tear film’s protective oily layer become blocked or do not function properly.

Improving Tear Film Stability

Improving tear film stability involves addressing its underlying causes, particularly MGD. One effective at-home treatment is applying warm compresses to the eyelids. The heat helps liquefy hardened oils clogging the meibomian glands, improving their flow. This can be followed by lid hygiene using specialized cleansers to remove debris from the eyelid margins.

Environmental and behavioral factors also play a role. For those who spend long hours on digital screens, practicing the “20-20-20” rule is beneficial. This involves taking a 20-second break every 20 minutes to look at something 20 feet away to encourage frequent blinking. Using a humidifier can add moisture to dry indoor air.

For evaporative dry eye, lipid-based or emulsion eye drops are designed to supplement the tear film’s oily layer. Nutritional supplements like omega-3 fatty acids may also support meibomian gland function.