Theirisis the colored part of the eye that controls the amount of light that enters into the eye.
It is the most visible part of the eye.
The iris lies in front of thecrystalline lensand separates the anterior chamber form the posterior chamber.
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The iris in part of the uveal tract which includes the ciliary body that also lies behind the iris.
The iris tissue makes up the pupil.
The pupil is the hole in the iris in which light passes through to the back of the eye.
Pupil Size
The size of the pupil is controlled by two muscles in the iris.
The sphincter pupillae surrounds the border of the pupil and when it contracts, the pupil decreases in size.
The second muscle that controls pupil size is the dilator pupillae.
This muscle contains fibers that are arranged in a radial pattern in the iris.
When it contracts, the pupil dilates or increases in size.
This is called mydriasis.
The parasympathetic system controls the sphincter pupillae and the sympathetic system controls the dilator pupillae.
Iris Color
Iris color depends on the amount ofmelanin pigmentin the iris.
However, the blue-eyed person has much less pigment.
The back of the iris is usually heavily pigmented to prevent light from shining through the iris.
The inheritance patterns of iris color is a heavily studied area.Eye coloris controlled by three basic genes.
Researchers understand two of those genes really well and one of them is still a bit of a mystery.
These genes control the development of green, brown andblue eye color.
Gray, hazel, and other combinations are more difficult to predict.
In genetics, this is termed “polygenic.”
Polygenic means that there may be several complicated genes involved that interact to createeye color.
The iris is in the uveal tract, which is the middle layer of the eye.
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