Tear Meniscus Height

Your tear film is extremely thin. But not all tears are spread evenly across the exposed surface of the eye. Some tear fluid collects along the edges of the eyelids, forming small curved reservoirs. These are the upper and lower tear menisci.

The lower tear meniscus is usually the easiest to examine and is the one most commonly measured. You can think of it as a small reservoir connected to the tear film. When the amount of tear fluid on the eye changes, the size of this reservoir can change too.

Tear meniscus height gives us information about tear volume. In simple terms: how much tear fluid appears to be available on the eye at this moment?

A smaller-than-expected tear meniscus may suggest that the volume of aqueous tear fluid on the ocular surface is reduced. That can be useful when investigating aqueous-deficient dry eye.

But there is an important distinction: tear volume is not the same thing as tear production.

Imagine a bathtub. The amount of water in the bathtub depends on more than how quickly water is coming from the tap. It also depends on how quickly water is leaving.

The tear system works in a similarly dynamic way. The amount of tear fluid present on the eye depends on a balance between tear secretion, tear distribution, evaporation and tear drainage.

So a small tear meniscus tells us that tear volume is low. It does not automatically tell us why.

There are several ways to assess it. A clinician may estimate the tear meniscus during a slit-lamp examination. Modern dry-eye instruments can also image the lower tear meniscus and measure its height more objectively. Some devices use optical coherence tomography (OCT) or other imaging techniques to examine the tear reservoir without touching the eye.

This is useful because the natural tear system can be easily disturbed. Ideally, we want to observe it before adding drops, dyes or other things that might change tear volume.

Usually not. When tear meniscus height is assessed visually or with non-invasive imaging, nothing needs to touch the ocular surface. You simply look into the instrument while the clinician examines or photographs the tear meniscus. This makes it very different from the Schirmer test, where a paper strip is placed inside the lower eyelid.

A low tear meniscus suggests that there is relatively little tear fluid present on the ocular surface. This can support the suspicion of aqueous deficiency. For example, if someone has a low tear meniscus, a very low Schirmer result and other findings consistent with reduced aqueous tears, those findings together may make aqueous deficiency much more likely.

But a low tear meniscus should still be interpreted as part of the whole picture.

No. It tells us about the amount of tear fluid present, not directly about the function of the lacrimal gland.

Reduced tear secretion is one possible explanation for low tear volume. But tear volume also depends on what happens to tears after they reach the ocular surface. That is why we should not automatically make the jump from “low tear meniscus” to “damaged lacrimal glands.” The measurement does not tell us that.

Not by itself. Tear meniscus height is useful for understanding the aqueous side of the tear system, but it is not one of the main homeostasis markers used by TFOS DEWS III to establish the general diagnosis of dry eye. Instead, it helps clinicians understand what may be contributing to the disease once dry eye is being evaluated.

This is similar to the distinction we made with Schirmer: “Does this person have dry eye?” and “Is reduced aqueous tear volume an important part of this person’s dry eye?” are two different questions.

These tests are related, but they do not measure the same thing.

Tear meniscus height looks at the tear reservoir that is already present on the eye. It provides information about tear volume at the time of measurement.

The Schirmer test measures how much of a paper strip becomes wet over several minutes. During that time, tears continue to be secreted, the strip absorbs fluid and the strip itself may stimulate reflex tearing. So Schirmer is a more invasive and dynamic test.

This is why someone can potentially have results from these two tests that do not appear to match perfectly. They are not asking exactly the same question.

Absolutely. A person may have an apparently normal amount of aqueous tear fluid but still have problems with:

• •tear-film stability
• •meibomian gland function
• •tear-film lipids
• •mucins or the glycocalyx
• •blinking
• •eyelid closure
• •the ocular surface
• •sensory nerve function

So normal tear volume does not mean a normal tear-film system. It only tells us that obvious reduction in tear volume was not detected by this particular measurement.

Yes. This sounds contradictory, but it becomes easier to understand once we separate everyday tear balance from reflex tearing.

An irritated ocular surface can sometimes trigger a burst of reflex tears. Your eyes may temporarily become visibly watery. But this does not necessarily mean that your normal tear volume is consistently adequate throughout the day. A short episode of tearing and the usual state of the tear film are not the same thing.

The tear system is dynamic. Blinking can redistribute tears. Recent eye drops can increase tear volume. Reflex tearing can temporarily enlarge the meniscus. Environmental conditions can influence the tear system. Drainage also changes the amount of fluid present. And the measurement technique itself can matter.

So, as with many dry-eye tests, one measurement is a snapshot. It should be interpreted together with the rest of the examination.

You may see numerical cut-offs in research papers or on dry-eye machines. But measurements can depend on the technique and device being used.

For a patient, the more useful question is usually not “Is my number above or below one universal cut-off?” but “Does my tear meniscus appear reduced, and does that finding agree with the rest of my aqueous-tear assessment?” That is much more clinically meaningful.

It can help estimate how much tear fluid is present on the ocular surface, and whether reduced tear volume may be part of your dry-eye picture. It can therefore be particularly useful when aqueous deficiency is suspected.

By itself, tear meniscus height cannot tell you:

• •why tear volume is low
• •how well your lacrimal glands are functioning
• •whether you have MGD
• •whether your tear film is stable
• •whether your ocular surface is damaged
• •whether you have dry eye disease at all

Those questions require other information.