What are the two main types of dry eye disease?

Aqueous-deficient dry eye, in which the lacrimal glands produce too few tears, and evaporative dry eye, in which tears evaporate too quickly, most often due to meibomian gland dysfunction. The two types frequently coexist.

Why do some people have severe dry eye symptoms but mild clinical signs?

Symptoms and signs of dry eye often diverge. Abnormalities in corneal nerve function (neurosensory mechanisms) are thought to contribute, which is why dry eye is classed as a multifactorial disease rather than a simple lack of tears.

Dry Eye Disease

Dry eye disease is a multifactorial disorder of the ocular surface in which loss of tear-film homeostasis leads to ocular discomfort, visual disturbance, and surface inflammation and damage. It is among the most common conditions seen in eye care and a frequent cause of chronic ocular symptoms.

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Definition

Dry eye disease is a multifactorial disease of the ocular surface characterised by a loss of homeostasis of the tear film, accompanied by ocular symptoms, in which tear-film instability and hyperosmolarity, ocular surface inflammation and damage, and neurosensory abnormalities play aetiological roles, as defined by the TFOS DEWS II report.

Scope

This entry covers the modern definition and classification of dry eye disease, its two principal subtypes (aqueous-deficient and evaporative), the self-perpetuating cycle of tear-film instability and inflammation, and its epidemiology. It is a reference overview and does not provide management or prescribing guidance.

Key concepts

Tear-film homeostasis
Tear hyperosmolarity
Aqueous-deficient versus evaporative dry eye
Meibomian gland dysfunction
Ocular surface inflammation
The vicious cycle of dry eye
Neurosensory abnormality and symptom-sign discordance

Mechanisms

The central mechanism described in the TFOS DEWS II framework is loss of tear-film homeostasis: reduced tear production or excessive evaporation raises tear osmolarity, which damages the ocular surface epithelium and activates inflammatory pathways. Inflammation in turn further destabilises the tear film and can impair the goblet cells and meibomian glands, creating a self-amplifying vicious cycle. Damage to corneal nerves contributes neurosensory abnormalities that may explain why symptoms and clinical signs frequently diverge. Evaporative disease (often from meibomian gland dysfunction) and aqueous-deficient disease (reduced lacrimal secretion, as in Sjogren syndrome) are the two overlapping mechanistic subtypes.

Clinical relevance

Dry eye disease is a leading reason for eye-care visits and a substantial source of reduced quality of life and visual function; understanding its definition and mechanisms underpins how clinicians appraise ocular surface symptoms. This entry is descriptive and for reference only, not a basis for diagnosis or treatment.

Epidemiology

Prevalence estimates vary widely with the definition used, ranging roughly from 5% to over 30% in different populations; the TFOS DEWS II epidemiology report identifies increasing age, female sex, Asian ethnicity, and environmental and digital-screen exposures among consistent risk factors. The wide range reflects heterogeneity in diagnostic criteria and the frequent mismatch between symptoms and signs.

History

The understanding of dry eye shifted over successive international workshops from a simple notion of 'tear deficiency' toward a multifactorial ocular surface disease. The TFOS Dry Eye Workshop reports, culminating in DEWS II (2017), consolidated the contemporary definition, classification into aqueous-deficient and evaporative subtypes, and the vicious-cycle model of tear-film instability and inflammation.

Debates

Discordance between symptoms and signs: Patient-reported symptoms and objective clinical signs of dry eye often correlate poorly, complicating diagnosis and outcome measurement; neurosensory abnormalities are one proposed explanation, and the issue remains an active methodological challenge.

Seminal works

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Frequently asked questions

What are the two main types of dry eye disease?: Aqueous-deficient dry eye, in which the lacrimal glands produce too few tears, and evaporative dry eye, in which tears evaporate too quickly, most often due to meibomian gland dysfunction. The two types frequently coexist.
Why do some people have severe dry eye symptoms but mild clinical signs?: Symptoms and signs of dry eye often diverge. Abnormalities in corneal nerve function (neurosensory mechanisms) are thought to contribute, which is why dry eye is classed as a multifactorial disease rather than a simple lack of tears.