Library · Anatomy
Cornea
Make it clearer
The cornea is the clear layer that sits farthest out in the eye, in front of the iris, which is the colored part, and of the pupil, the black opening in the center. It is the eye's front window: it has to focus light and, above all, let it through. The first bending of the light coming in, refraction, happens right there, and then the lens finishes focusing it onto the retina.
It is not a single sheet: it has five layers. From the outside in they are the epithelium, Bowman membrane, the stroma, Descemet membrane, and the endothelium. The last one, the endothelium, does a quiet and decisive job: it pumps the excess fluid out of the stroma, and that is how the cornea stays clear.
And there is something striking: the cornea does not have a single blood vessel. Precisely because it needs to be transparent. It is nourished by diffusion, taking what it needs from the tears on the outside and from the aqueous humor, the fluid that sits behind it, on the inside.
In brief
The cornea is the clear outermost layer of the eye, in front of the iris and pupil, and performs the first refraction of light.
It is the eye's front window: it has to focus light and, above all, let it through.
It has five layers: epithelium, Bowman membrane, stroma, Descemet membrane, and endothelium; the endothelium pumps excess fluid out of the stroma and maintains transparency.
To preserve that transparency the cornea has no blood vessels: it is nourished by diffusion from the tears and from the aqueous humor.
Sources (1)
- National Center for Biotechnology Information, StatPearls PublishingAnatomy, Head and Neck, Eye Cornea, StatPearlsPublished
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