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Introducing the blood-tear barrier: Structure, function, and disruption in ocular surface homeostasis
Marlies Gijs1, Li Liang1, Fleur Goezinne2
1University Eye Clinic Maastricht, Mental Health and Neuroscience Research Institute (MHeNs), Maastricht University, Maastricht, the Netherlands.
Progress in Retinal and Eye Research
|July 11, 2026
Summary
The blood-tear barrier (BTB) selectively controls what enters the tear film from blood vessels. This review models the BTB's structure and discusses its protective roles and how it can be disrupted.
Area of Science:
- Ophthalmology
- Physiology
- Molecular Biology
Background:
- Tear fluid composition differs from blood, implying a selective blood-tear barrier (BTB).
- The BTB's structure, function, and disruption mechanisms are poorly understood.
- Existing literature suggests a BTB regulates molecular exchange between ocular vasculature and tear film.
Purpose of the Study:
- To propose a conceptual model of the blood-tear barrier (BTB).
- To review the BTB's structure, functional roles, and disruption mechanisms.
- To highlight the importance of BTB integrity for ocular surface health.
Main Methods:
- Literature review and synthesis of current evidence.
- Development of a conceptual model for the BTB.
- Analysis of factors affecting BTB integrity.
Main Results:
- The BTB is proposed to consist of three compartments: tear film, epithelial layer, and vascular endothelium.
- Tight junctions are central to maintaining BTB integrity.
- The BTB provides bidirectional protection, shielding the eye and limiting blood-derived factor entry.
Conclusions:
- The BTB plays a crucial role in ocular surface protection.
- Disruption of the BTB can occur due to various factors like surgery, drugs, and diseases.
- Further understanding of the BTB is vital for ocular health and disease management.
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