Tear-Film Stability: Why Making Tears Is Only Part of the Job
When we think about dry eye, it is natural to focus on quantity. Does the eye produce enough tears?
That question matters, particularly in oGVHD, where lacrimal gland damage can cause profound aqueous tear deficiency. But the amount of fluid present is only one part of normal tear function.
The tear film must also remain stable.
With every blink, the eyelids spread a thin layer of tears across the cornea. For the next several seconds, that layer becomes the eye’s outermost optical and protective surface. It reduces friction, nourishes and protects epithelial cells, and creates the smooth interface needed for clear vision.
A healthy tear film is able to remain relatively intact until the next blink.
When it becomes unstable, dry areas can begin to appear sooner. Portions of the corneal surface are exposed, optical quality becomes less consistent, and the eye may respond with irritation or an increased urge to blink.
In oGVHD, several changes can push the tear film toward instability at the same time.
If the lacrimal glands produce too little aqueous fluid, there is less volume available to cover the surface. If the meibomian glands are not supplying an effective lipid layer, evaporation may accelerate. If conjunctival goblet cells are impaired, the mucin components that help tears interact with the ocular surface may also be affected.
This is why two patients can both be described as having “dry eyes” while the biology underneath that description is different.
One may be dominated by severe aqueous deficiency. Another may have a combination of low production and rapid evaporation. Another may produce measurable tears that nevertheless fail to form a stable and durable surface.
Clinicians can evaluate tear-film stability using measures such as tear breakup time. After a blink, they observe how long it takes for the tear layer to begin breaking apart.
The measurement provides useful information, but the concept itself is even more important.
A tear must do more than arrive at the eye. It must remain there, spread correctly, interact with the ocular surface, and continue protecting the cornea between blinks.
Tear-film instability can also affect vision. Because the tear film forms the first refractive surface encountered by incoming light, an irregular tear layer can cause visual quality to fluctuate. A blink may temporarily restore clarity, followed by increasing blur as the tear film breaks apart again.
For patients with oGVHD, that can make the disease feel unpredictable. Vision and comfort can vary not only from day to day, but from one blink to the next. Understanding tear-film stability therefore expands the conversation beyond whether an eye is simply wet or dry.
The better question is whether the tear system is creating the stable, protective environment that the ocular surface needs.
This article is for educational purposes only and is not medical advice.
Sources:
- Craig JP, Nichols KK, Akpek EK, et al. “TFOS DEWS II Definition and Classification Report.” The Ocular Surface, 2017.
https://www.tfosdewsreport.org/report-definition_and_classification/48_36/en/ - Wolffsohn JS, Arita R, Chalmers R, et al. “TFOS DEWS II Diagnostic Methodology Report.” The Ocular Surface, 2017.
https://www.tfosdewsreport.org/public/images/TFOS_DEWS_II_Diagnostic_method.pdf - Inamoto Y, Valdés-Sanz N, Ogawa Y, et al. “Ocular Graft-versus-Host Disease after Hematopoietic Cell Transplantation.” Biology of Blood and Marrow Transplantation, 2019.
https://pmc.ncbi.nlm.nih.gov/articles/PMC6362842/
