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. 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. The iris controls the pupil size.The pupil is actually located with its center a little below and slightly to the nasal side of the center of the cornea.
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Pupil Size
The parasympathetic system controls the sphincter pupillae and the sympathetic system controls the dilator pupillae. There is a connection between these muscles in that that the dilator muscle must relax to allow the sphincter to constrict the pupil. Normal pupil size ranges from 2 to 4 mm in diameter in the light to 4 to 8 mm in the dark.
Iris Color
Iris color depends on the amount ofmelanin pigmentin the iris. A person with brown eyes has the same color of melanin pigment that a person with a blue eye has. 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.
Abnormalities of the Iris & Pupil
Iris and pupil disorders include:
Frequently Asked QuestionsThe iris helps control the amount of light that reaches the retina in the back of the eye. Muscles in the iris allow the pupil to dilate (widen) to let in more light and constrict (narrow) to let in less light.The iris is in the uveal tract, which is the middle layer of the eye. It lies behind the cornea and in front of the lens, which both help to focus light on the back of the eye.Learn MoreAnatomy of the Eye
Frequently Asked Questions
The iris helps control the amount of light that reaches the retina in the back of the eye. Muscles in the iris allow the pupil to dilate (widen) to let in more light and constrict (narrow) to let in less light.
The iris is in the uveal tract, which is the middle layer of the eye. It lies behind the cornea and in front of the lens, which both help to focus light on the back of the eye.Learn MoreAnatomy of the Eye
The iris is in the uveal tract, which is the middle layer of the eye. It lies behind the cornea and in front of the lens, which both help to focus light on the back of the eye.
Learn MoreAnatomy of the Eye
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4 SourcesVerywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.National Eye Institute.About the Eye.McDougal DH, Gamlin PD.Autonomic control of the eye. Compr Physiol. 2015;5(1):439-73. doi:10.1002/cphy.c140014Reinhold HA, West MP.Nervous System. Acute Care Handbook for Physical Therapists, 4th edition.2014;6:123-160. doi:10.1016/B978-1-4557-2896-1.00006-8American Academy of Ophthalmology.Eye anatomy: Parts of the eye and how we see.
4 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.National Eye Institute.About the Eye.McDougal DH, Gamlin PD.Autonomic control of the eye. Compr Physiol. 2015;5(1):439-73. doi:10.1002/cphy.c140014Reinhold HA, West MP.Nervous System. Acute Care Handbook for Physical Therapists, 4th edition.2014;6:123-160. doi:10.1016/B978-1-4557-2896-1.00006-8American Academy of Ophthalmology.Eye anatomy: Parts of the eye and how we see.
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
National Eye Institute.About the Eye.McDougal DH, Gamlin PD.Autonomic control of the eye. Compr Physiol. 2015;5(1):439-73. doi:10.1002/cphy.c140014Reinhold HA, West MP.Nervous System. Acute Care Handbook for Physical Therapists, 4th edition.2014;6:123-160. doi:10.1016/B978-1-4557-2896-1.00006-8American Academy of Ophthalmology.Eye anatomy: Parts of the eye and how we see.
National Eye Institute.About the Eye.
McDougal DH, Gamlin PD.Autonomic control of the eye. Compr Physiol. 2015;5(1):439-73. doi:10.1002/cphy.c140014
Reinhold HA, West MP.Nervous System. Acute Care Handbook for Physical Therapists, 4th edition.2014;6:123-160. doi:10.1016/B978-1-4557-2896-1.00006-8
American Academy of Ophthalmology.Eye anatomy: Parts of the eye and how we see.
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