Library · Physiology
The tear film
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Your eyes are covered at all times by an extremely thin layer of fluid, the tear film. It is not just for crying: it lubricates the surface of the eye, protects it from the environment, and leaves it smooth so that light refracts properly.
It is not just any fluid, but three layers stacked one on top of another. The innermost is the mucin layer; the aqueous layer sits in the middle; and on the outside there is a layer of oil, which in medicine is called the lipid layer. Think of three coats of paint, one on top of another, each with its own job.
Most of those lipids are produced by the meibomian glands, which sit along the eyelid margin, and the job of that layer is to slow the evaporation of the tears.
The aqueous layer, in turn, carries defenses of its own: proteins such as lysozyme and lactoferrin.
In brief
The tear film coats the surface of the eye: it lubricates it, shields it from the environment, and leaves a smooth surface for refracting light.
It has three layers: an inner mucin layer, a middle aqueous layer, and an outer lipid layer.
Three coats of paint, one on top of another, each with its own job.
Most of those lipids come from the meibomian glands along the eyelid margin, and that layer slows evaporation.
The aqueous layer carries defenses such as lysozyme and lactoferrin.
Sources (1)
- National Center for Biotechnology Information, StatPearls PublishingBiochemistry, Tear Film, StatPearlsPublished
This page explains the topic in general terms; it does not tell anyone what treatment to follow.
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