Dry eye syndrome is a chronic condition in which the tear film no longer protects and lubricates the surface of the eye. Clinicians now use the term dry eye disease. The 2025 Tear Film and Ocular Surface Society Dry Eye Workshop (TFOS DEWS III) defines it as a multifactorial, symptomatic disease marked by a loss of homeostasis of the tear film or ocular surface, and states that it is a disease and not a syndrome [1].
The condition is common. Published prevalence ranges from 5% to 50% depending on the population and the criteria used, and it rises with age [2]. Symptoms alone are not enough for a diagnosis, so clinics combine a questionnaire with objective tests of the tear film.
Symptoms and Dry Eye Causes
The typical symptoms are a scratchy or gritty feeling, stinging or burning, redness, sensitivity to light and blurred vision [3]. In dry eye disease, the lacrimal glands produce too little tear fluid, the tears evaporate too quickly, or the tears do not work well enough to keep the surface wet [3].
The main dry eye causes and risk factors are:
- Age and sex. Prevalence increases with age, and women are affected more often than men [2].
- Ethnicity. Asian ethnicity is a consistent risk factor in population studies [2].
- Contact lens wear and screen use. Both are linked to dry eye, and prolonged screen time is a recognised trigger [3].
- Autoimmune disease. Sjögren syndrome and lupus raise the risk [3].
- Environment and medicines. Smoke, wind and air conditioning aggravate symptoms, and some systemic medicines can cause dry eye [3].
The Tear Film and the Two Types of Dry Eye
The tear film is described as a two-phase structure. A thin outer lipid layer lies over a mucoaqueous layer that contains water, mucins, proteins and electrolytes [4]. The lipid layer comes from meibum, an oil secreted by the meibomian glands at the eyelid margin and spread across the eye with each blink [4].
This structure explains the two main subtypes of dry eye [5]:
- Aqueous deficient dry eye. The lacrimal glands produce too little of the watery component, so tear volume is low.
- Evaporative dry eye. Tear volume may be adequate, but the tears evaporate too quickly. Meibomian gland dysfunction and a poor lipid layer are the usual findings.
Many patients show features of both, which is why testing looks at tear stability, tear volume and the lipid layer together [5].
How a Dry Eye Test Confirms the Diagnosis
There is no single dry eye test. TFOS DEWS III sets out a two-step diagnosis: a positive symptom score, plus at least one objective sign that the tear film or ocular surface has lost its normal balance [1].
| Step | Test | Result that supports dry eye |
| Symptoms | OSDI-6 questionnaire | Score of 4 or more |
| Sign | Non-invasive tear break-up time | Under 10 seconds |
| Sign | Tear osmolarity | 308 mOsm/L or more, or a difference of more than 8 mOsm/L between eyes |
| Sign | Ocular surface staining | More than 5 corneal spots, more than 9 conjunctival spots, or lid margin staining at least 2 mm long and 25% wide |
A positive questionnaire with any one of the three signs gives a diagnosis of dry eye disease [1]. The earlier TFOS DEWS II criteria used the same sign thresholds with the full OSDI (score of 13 or more) or the DEQ-5 questionnaire [5].
Once the diagnosis is made, further tests identify the subtype. Meibomian gland assessment, lipid layer evaluation and tear volume measurement show whether the disease is mainly evaporative or aqueous deficient, and this guides treatment [5].
Tear Break-Up Time and Tear Film Stability
Tear break-up time is the interval between a complete blink and the first dry spot in the tear film. A short interval means the tear film is unstable.
It can be measured in two ways:
- Fluorescein break-up time. A dye is instilled and the clinician times the first dark spot under the cobalt blue light of a slit lamp. The dye itself can disturb the tear film.
- Non-invasive break-up time (NIBUT). An instrument projects a pattern onto the tear film and records when the reflection first distorts. Nothing touches the eye.
TFOS guidance prefers the non-invasive method and uses a cut-off of under 10 seconds [1,5].
Imaging Tests That Measure the Tear Film
Imaging lets a clinic assess the tear film without dyes or contact, and keeps a record for follow-up.
Lipid layer interferometry. Light reflected from the front and back of the lipid layer produces coloured interference patterns. The colours and their spread indicate how thick and how even the layer is. In a study using an ocular surface interferometer, a lipid layer thickness of 75 nm or less detected meibomian gland dysfunction with 65.8% sensitivity and 63.4% specificity. A cut-off of 60 nm or less gave 47.9% sensitivity and 90.2% specificity [6]. These figures show that lipid layer interferometry is informative but is read alongside other findings, not on its own.
Tear meniscus height. The strip of tears along the lower lid margin is imaged and measured. A low meniscus points to reduced tear volume and aqueous deficiency [5].
Meibography. Infrared imaging of the eyelids shows the meibomian glands and any gland loss, which supports a diagnosis of evaporative dry eye [5].
Automated analysis is making these tests more consistent. The FH-POISE platform from Forus Health analyses lipid layer interferometry video frame by frame. It reports blink frequency, the interval between blinks, lipid layer thickness and a grade on an established reference scale [7].
Conclusion
Dry eye syndrome is diagnosed from symptoms and signs together. A validated questionnaire is followed by a test of tear film stability, osmolarity or surface staining, and then by tests that identify the subtype. Tear break-up time shows how stable the tear film is. Lipid layer interferometry, tear meniscus height and meibography show why it is unstable. That distinction between evaporative and aqueous deficient disease is what allows treatment to be matched to the cause.
This article is for general information and does not replace an examination by a qualified eye care professional.
References
- Wolffsohn JS, et al. TFOS DEWS III: Diagnostic Methodology. Am J Ophthalmol. 2025;279:387-450. doi:10.1016/j.ajo.2025.05.033
- Stapleton F, Alves M, Bunya VY, et al. TFOS DEWS II Epidemiology Report. Ocul Surf. 2017;15(3):334-365. doi:10.1016/j.jtos.2017.05.003
- National Eye Institute. Dry Eye. Last updated 6 August 2025. nei.nih.gov
- Willcox MDP, Argüeso P, Georgiev GA, et al. TFOS DEWS II Tear Film Report. Ocul Surf. 2017;15(3):366-403. doi:10.1016/j.jtos.2017.03.006
- Wolffsohn JS, Arita R, Chalmers R, et al. TFOS DEWS II Diagnostic Methodology report. Ocul Surf. 2017;15(3):539-574. doi:10.1016/j.jtos.2017.05.001
- Finis D, Pischel N, Schrader S, Geerling G. Evaluation of lipid layer thickness measurement of the tear film as a diagnostic tool for Meibomian gland dysfunction. Cornea. 2013;32(12):1549-1553.
- Forus Health. Lipid Layer Interferometry (LLI). forushealth.com
