The stroma of the iris is a
fibrovascular layer of tissue. It is the upper layer of two in the
iris.
Structure
The
stroma is a delicate interlacement of fibres. Some circle the circumference of the iris and the majority radiate toward the
pupil.
Blood vessels and
nerve
A nerve is an enclosed, cable-like bundle of nerve fibers (called axons) in the peripheral nervous system.
A nerve transmits electrical impulses. It is the basic unit of the peripheral nervous system. A nerve provides a common pathway for the e ...
s intersperse this mesh.
In dark eyes, the stroma often contains
pigment granules. Blue eyes and the eyes of
albinos, however, lack pigment.
The stroma connects to a
sphincter muscle (
sphincter pupillae), which contracts the
pupil in a circular motion, and a set of dilator muscles (
dilator pupillae
The iris dilator muscle (pupil dilator muscle, pupillary dilator, radial muscle of iris, radiating fibers), is a smooth muscle of the eye, running radially in the iris and therefore fit as a dilator. The pupillary dilator consists of a spokelike ...
) which pull the iris radially to enlarge the pupil, pulling it in folds. The back surface is covered by a commonly, heavily pigmented
epithelial layer that is two cells thick (the iris pigment epithelium), but the front surface has no epithelium. This anterior surface projects as the muscles dilate.
References
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External links
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Human iris
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