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Dry eye disease
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Dry eye happens when the eyes do not make enough tears to stay moist, or when the tears they do make do not do their job well. Normally, glands above the eyes produce those tears.
And a tear is not just water. It is a film of three layers: a lipid layer, meaning fatty, an aqueous one, and a mucin one, the sticky layer that clings to the surface of the eye. The fatty layer is made by the meibomian glands, which line the edge of the eyelids, and their oil reduces tear evaporation. It is the oil cap that keeps what is underneath from evaporating.
When that balance breaks down, the tears become concentrated: they end up with too much dissolved salt for the water they have left, and that is called hyperosmolarity. That is the hallmark of the disease. And that concentrated tear is not harmless: it sets off a cascade of signals that releases inflammatory mediators onto the surface of the eye. That is why dry eye is not just a lack of tears: there is also inflammation on the surface of the eye.
In brief
Dry eye happens when the eye does not make enough tears to stay moist, or when the tears it does make do not work properly.
The tear film has three layers, lipid, aqueous and mucin; the meibomian glands supply the oil that slows evaporation.
The tear is a three-layer film, and the top layer is the oil cap that keeps it from evaporating.
Its hallmark is hyperosmolarity of that film, which triggers inflammatory mediators on the ocular surface.
Sources (2)
- National Eye InstituteDry Eye, National Eye InstitutePublished
- National Center for Biotechnology Information, StatPearls PublishingDry Eye Syndrome, StatPearlsPublished
This page explains the topic in general terms; it does not tell anyone what treatment to follow.
Updated