How Is Dry Eye Diagnosed?

The first piece of the puzzle is how your eyes feel and how they behave in everyday life. Dry eye can cause many different symptoms, including:

• •dryness
• •burning or stinging
• •grittiness or a feeling that something is in the eye
• •tired or uncomfortable eyes
• •fluctuating or blurry vision
• •sensitivity to wind or dry air
• •watery eyes

A doctor may also use a short questionnaire to understand how often these symptoms occur and how much they affect daily life.

But symptoms alone cannot prove that you have dry eye. Many other eye conditions can feel similar. So symptoms tell us: “Something may be wrong.” They don’t yet tell us exactly what is wrong.

Dry Eye Symptoms: what they can — and can't — tell you

Before calling a problem dry eye, a clinician should consider whether another condition could explain the symptoms. This is called differential diagnosis, but the idea is simple: what else could make the eyes feel this way?

That matters because burning, redness, watering, irritation and pain are not unique to dry eye. Sometimes another condition is responsible. Sometimes dry eye and another problem exist at the same time.

This is why a proper evaluation includes your history and an examination of the eyes — not just a machine test.

Conditions That Can Look Like Dry Eye

If the symptoms are compatible with dry eye, the next step is to look for objective evidence that the tear film or ocular surface is no longer maintaining its normal balance. Doctors sometimes call this loss of homeostasis.

That phrase sounds complicated, but it simply means: the system is no longer able to keep the tear film and ocular surface stable and healthy in the way it normally should.

There are several ways to look for this.

Does the tear film stay stable between blinks?

After you blink, the tears should spread across the eye and remain reasonably stable until the next blink. A doctor can measure how quickly the tear film begins to break apart. This is called tear breakup time. If the tear film breaks up unusually quickly, it tells us that the tear film is unstable. But it does not yet tell us why.

Are the tears becoming too concentrated?

Doctors can also measure tear osmolarity. The name sounds technical, but the idea is straightforward. When the balance of water and dissolved substances in the tears becomes abnormal, the tears can become unusually concentrated. That can be another sign that the tear system has lost its normal balance.

Is the ocular surface becoming damaged or stressed?

A doctor can place a small amount of special dye in the eye. The dye can reveal areas where the surface of the cornea or conjunctiva is not completely healthy. This is called ocular-surface staining. The pattern and amount of staining can provide useful information about what is happening on the surface of the eye.

We look at all of these tests separately later in this chapter. For now, you don’t need to remember the numbers or medical thresholds. The important thing is to understand what each test is trying to tell us.

In the current TFOS DEWS III approach, the basic idea is:

dry-eye symptoms→objective evidence of lost homeostasis→dry eye disease

But even here, one test does not tell the entire story. A positive finding may provide evidence of dry eye, while a normal result on one particular test does not necessarily rule it out. Different tests examine different parts of the system.

This is why a good dry-eye evaluation usually looks at the overall pattern, rather than relying on one number.

Once dry eye has been established, the investigation is not finished. In many ways, this is where it becomes more useful. Now we want to know what is actually going wrong:

• •Is the lipid part of the tear film abnormal?
• •Is there too little aqueous tear fluid?
• •Is the tear film interacting poorly with the ocular surface?
• •Are the meibomian glands functioning normally?
• •Is blinking incomplete? Are the eyelids closing properly?
• •Is the ocular surface damaged?
• •Is inflammation important?
• •Could sensory nerve function be involved?

There may be one dominant problem — or several interacting problems. This is called subclassification. But in patient language, we could simply call it: finding the drivers.

Many patients know the Schirmer test as “the dry-eye test.” It is the test where a small paper strip is placed near the lower eyelid to see how much it becomes wet.

But Schirmer does not tell us whether the entire dry-eye system is normal or abnormal. It mainly gives information about aqueous tear production. That can be very useful if we are trying to understand whether insufficient aqueous tears are part of the problem.

But someone can have a normal Schirmer result and still have dry eye. For example, their main problem may involve tear-film lipids, blinking, the ocular surface or another mechanism. So Schirmer answers one question, not every question.

Meibography takes images of the meibomian glands inside the eyelids. It can show their structure and whether there has been visible gland loss or other changes.

Again, this can be extremely useful. But it answers a specific question: what do the meibomian glands look like? It does not, by itself, tell us whether someone has dry eye or explain everything about how those glands are functioning. A gland image is one piece of the puzzle.

A clinician may also gently press on the glands to see whether meibum comes out and what it looks like. Is it easy to express? Is it clear and fluid? Is it thick? Is very little coming out?

This gives information about meibomian gland function and meibum quality. Again, it can help identify an important driver of dry eye. But it is not a complete dry-eye diagnosis by itself.

Modern clinics may use devices that produce impressive reports containing many measurements: tear breakup time, tear meniscus height, lipid-layer images, meibography, redness, blink analysis and other information.

These technologies can be very useful. But the report still needs to be interpreted. A machine can measure different pieces of the system. It cannot turn every abnormal number into the explanation for your symptoms. The real task is to understand how those pieces fit together.

Ideally, you should leave an evaluation with a clearer understanding of three things:

• •Do I have dry eye disease?
• •Which parts of my tear-film, eyelid and ocular-surface system are abnormal?
• •Which of those problems seem most important in my case?

That third question matters enormously. Because eventually treatment should be aimed at a problem that has actually been identified, rather than chosen simply because it is a popular dry-eye treatment.