What they can — and can’t — tell you.
One of the confusing things about dry eye is that it does not always feel the way its name suggests.
Some people describe obvious dryness. Others mainly experience burning. Some feel grittiness, heaviness or tired eyes. Some notice fluctuating vision. Some have eyes that water constantly. And for some people, pain is the dominant problem.
So symptoms are extremely important — but they do not necessarily tell us which part of the dry-eye system is going wrong.
People with dry eye may describe:
Not everyone experiences all of these. And different people can experience the same underlying problem very differently.
This sounds contradictory, but it isn’t.
If the ocular surface becomes irritated or unstable, the nervous system can trigger reflex tearing. The eyes may suddenly produce a large amount of watery tears in response.
But reflex tearing does not necessarily mean that the normal tear film is functioning well. The tear film still needs the right composition, distribution and stability to protect the ocular surface between blinks.
So watery eyes do not automatically mean that dry eye can be ruled out.
The tear film is not only there for comfort. It is also the first optical surface that light passes through when it enters the eye. If that surface becomes irregular between blinks, vision can fluctuate.
A common clue is vision that becomes less clear and then temporarily improves after blinking. That does not prove dry eye by itself, but it can provide useful information about tear-film stability.
The way symptoms behave can sometimes help guide the investigation. For example:
These patterns can provide useful clues. But they are clues, not diagnoses.
This is one of the most important things to understand.
Feeling very dry does not necessarily mean that you have too little aqueous tear fluid. Burning does not automatically mean inflammation. Watery eyes do not automatically mean that tear production is normal. Pain does not automatically tell us how damaged the ocular surface is. And discomfort during screen use does not automatically mean that screens caused the disease.
Different problems can produce similar sensations. That is why symptoms cannot reliably tell us whether the main problem involves tear-film lipids, aqueous tears, mucins or the glycocalyx, blinking, eyelid closure, the ocular surface, inflammation, nerves — or several of these together.
To understand that, we need examination and testing.
This is extremely common in dry eye. Some people have severe symptoms but relatively few abnormalities on routine clinical tests. Others have obvious ocular-surface changes but surprisingly little discomfort.
This is known as sign–symptom discordance. And it is now well recognized in dry-eye research. There are several reasons why this can happen.
The tear film is a dynamic system. It changes with blinking, environment, humidity, airflow, screen use, time of day, contact-lens wear and recent use of eye drops. Your symptoms may also fluctuate from hour to hour or day to day.
A clinic test, however, measures what is happening during a relatively short period of time. So the eye that a doctor examines at 10 a.m. in a quiet clinic may not behave exactly like the same eye after eight hours of work in a dry room. That does not make the test useless. It simply means that a single measurement is a snapshot of a changing system.
The ocular surface contains a very dense network of sensory nerves. As we discussed in Neural Dysfunction & Altered Sensation, these nerves detect changes at the surface of the eye and help produce sensations as well as reflex responses such as tearing and blinking.
If sensory processing changes, the relationship between surface damage and symptoms can change too. In some situations, the nervous system may become unusually sensitive. Symptoms may then be much stronger than we would expect from routine ocular-surface findings. In other situations, corneal sensitivity may be reduced. The eye may then show significant surface abnormalities while producing surprisingly few symptoms.
This is one reason why how dry an eye feels is not a direct measurement of how much tear fluid is present or how damaged the surface is.
This deserves special emphasis.
If someone has significant symptoms but routine dry-eye tests show relatively little, it does not automatically mean that the symptoms are imaginary or unimportant. It means that the explanation may not yet be complete.
There may be subtle tear-film abnormalities. There may be another ocular-surface condition. Sensory nerve function may be involved. There may be more than one problem at the same time. Or the tests performed may simply not have captured what happens during the patient’s normal day.
The next step should be to understand the mismatch — not simply dismiss it.
The opposite mistake is also possible. Very severe eye symptoms do not automatically prove that severe dry eye disease is present.
Other ocular conditions can cause similar symptoms. And significant pain — particularly when it seems very different from the visible ocular-surface findings — may require investigation beyond routine dry-eye testing.
This is why symptoms always need to be interpreted together with the examination.
The reverse can happen too. Some people have significant ocular-surface abnormalities while experiencing relatively little discomfort. Reduced corneal sensitivity is one possible explanation. Age and certain ocular or systemic conditions can also affect sensation.
So “My eyes don’t feel very dry” does not necessarily mean “My ocular surface is completely healthy.” This can be particularly important when significant ocular-surface disease is discovered during an eye examination.
You may be asked to complete a questionnaire about your symptoms. This is not simply paperwork. A questionnaire provides a standardized way of recording how often symptoms occur, how severe they are, and how much they interfere with everyday activities.
The latest TFOS DEWS III recommendations use a short questionnaire called the OSDI-6 as the preferred symptom-screening tool for dry eye. But the questionnaire still does not tell the doctor what is causing the symptoms. It is one part of the diagnostic process.
The fact that symptoms cannot diagnose the mechanism does not make them unimportant. Quite the opposite. Your experience contains information that a five-minute examination cannot capture. It can be useful to notice patterns such as:
These observations can help your clinician decide what needs to be investigated. The goal is not to diagnose yourself from the pattern. The goal is to provide another piece of the puzzle.
This may be the easiest way to think about it. Symptoms tell us what you are experiencing. Signs and tests tell us what we can currently measure or observe.
Neither should automatically cancel out the other. If they fit together well, the picture may be relatively straightforward. If they do not, the mismatch itself may be important information.
TFOS DEWS III: Diagnostic Methodology.
Current evidence-based guidance on dry-eye symptoms, symptom screening, differential diagnosis and the sometimes poor relationship between symptoms and clinical signs.
TFOS DEWS III: Digest.
Updated review of dry-eye pathophysiology, pain and sensation, tear-film function and other factors influencing the relationship between symptoms and signs.
TFOS DEWS II: Pain and Sensation Report.
Detailed review of corneal sensory nerves, ocular discomfort and pain mechanisms relevant to dry eye.