The Schirmer Test

A narrow strip of special filter paper is folded at one end and placed over the edge of the lower eyelid. The strip remains there, usually for five minutes. Tears travel along the paper and wet it. At the end of the test, the clinician measures the length of the wet area in millimeters.

So the number on your result is literally: how many millimeters of paper became wet during the test.

The Schirmer test is mainly useful when we want to investigate the aqueous part of the tear system. Aqueous tears make up most of the volume of the tear film and are produced largely by the lacrimal glands and associated tear-producing tissues.

If very little of the strip becomes wet, this can provide evidence that aqueous tear availability is reduced. This can be particularly important when a clinician suspects aqueous-deficient dry eye.

But there is an important complication.

Think about what happens during the test. A piece of paper is sitting against a very sensitive part of the eye for several minutes. Your eye can feel it. And irritation of the ocular surface can stimulate the nervous system to produce reflex tears. These are the extra tears your eyes produce in response to irritation.

So the Schirmer test does not necessarily measure only the quiet, everyday tear secretion that normally maintains your tear film. The test itself can influence the result. This is one reason Schirmer measurements can vary.

Sometimes anesthetic eye drops are used before the test. The idea is to reduce the irritation caused by the strip and therefore reduce reflex tearing. You may hear this described as an attempt to measure more “basal” tear secretion.

But even this distinction is not perfect. Current TFOS guidance notes that variations of the Schirmer test — including the use of topical anesthetic — have limitations in repeatability and diagnostic performance.

So it is better not to think of “without anesthetic = total tears” and “with anesthetic = pure basal tears” as two perfectly precise measurements. The biology — and the test — are more complicated than that.

There are several reasons. The strip itself can stimulate tearing. Its exact position can matter. Closing or opening the eyes during testing may influence conditions. Environmental factors may matter. The natural tear system also changes over time. And different versions of the test may be performed differently.

This means that a Schirmer result should not be treated as though it were a perfectly fixed measurement of how many tears your eyes are capable of producing. It is one measurement taken under particular testing conditions.

A clearly low result can be an important clue that aqueous tear deficiency may be present. This becomes especially meaningful when it fits with other findings. For example, the clinician may also look at:

• •tear meniscus height
• •ocular-surface staining
• •tear-film stability
• •symptoms
• •the patient’s medical history

If several pieces of information point toward reduced aqueous tear availability, the case becomes much stronger than if we rely on the Schirmer result alone.

Not necessarily. This is an important distinction.

A low Schirmer result tells us that little wetting occurred during that particular test. It does not tell us exactly why. It does not provide an image of the lacrimal gland. And it does not, by itself, prove that the gland is permanently damaged or unable to function.

If significant aqueous deficiency is suspected, the next question is why it is happening. That requires the wider clinical picture.

No. This is probably the biggest misunderstanding surrounding the test. A person can have plenty of aqueous tear fluid and still have dry eye. Their main problem might involve:

• •tear-film lipids
• •meibomian gland dysfunction
• •mucin or glycocalyx abnormalities
• •tear-film instability
• •blinking
• •eyelid closure
• •the ocular surface
• •another mechanism

So a normal Schirmer result does not mean a normal tear-film system. It only tells us that this particular test did not show markedly reduced tear wetting under those testing conditions.

Not by itself. In the current TFOS DEWS III diagnostic framework, Schirmer is not one of the primary tests used to establish the general diagnosis of dry eye disease. Instead, the main diagnostic markers look for evidence that tear-film or ocular-surface homeostasis has been lost — through tear-film instability, abnormal tear concentration and ocular-surface staining.

Schirmer becomes particularly useful later when the clinician is trying to determine whether aqueous deficiency is one of the drivers.

This is a very useful distinction: diagnosing dry eye is not exactly the same thing as identifying aqueous deficiency.

These two tests are sometimes grouped together because both relate to aqueous tears. But they measure different things.

The tear meniscus is the small reservoir of tears sitting along the lower eyelid. Measuring its height gives us information about how much tear fluid appears to be present on the eye at that moment.

Schirmer, on the other hand, measures how much of a paper strip becomes wet over several minutes. During those minutes, tears are being produced, distributed and absorbed by the strip — and the strip itself may stimulate additional tearing.

So tear meniscus height reflects tear volume present, while Schirmer reflects tear wetting during a timed, invasive test. They are related, but they are not interchangeable.

Although Schirmer has limitations, very low values can still be clinically important. A markedly low result — especially when it is repeatable and fits with other findings — can strengthen the suspicion of significant aqueous deficiency. This may prompt a clinician to investigate further.

For example, severe aqueous deficiency can sometimes occur in association with systemic conditions such as Sjögren’s disease. That does not mean that everyone with a low Schirmer result has Sjögren’s. It means that the result can become one clue within a much larger medical picture.

Because a test can have limitations and still be useful. Schirmer is inexpensive. It is widely available. It requires little specialized equipment. And very low tear wetting can provide clinically valuable information.

The important thing is to understand what kind of information the test provides and not ask it to answer questions it was never designed to answer.

It can help identify whether reduced aqueous tear availability may be part of your dry-eye picture. A very low result can be particularly informative when it agrees with other findings. It can therefore help clinicians identify aqueous deficiency as a possible driver.

By itself, it cannot tell you:

• •whether you have dry eye disease
• •whether your meibomian glands are functioning normally
• •whether the lipid component of your tear film is healthy
• •whether your tear film is stable
• •why aqueous tear availability may be reduced
• •whether your lacrimal glands are permanently damaged

And because the test itself can stimulate tearing, the number should not be interpreted as a perfectly precise measurement of your normal everyday tear production.