Table of ContentsView AllTable of ContentsAnatomyFunctionAssociated ConditionsTesting
Table of ContentsView All
View All
Table of Contents
Anatomy
Function
Associated Conditions
Testing
The iris is the colored part of your eye. It is the muscular curtain that sits near the front between the cornea and the lens. The iris determines the size of thepupil(the small, black opening) to regulate how much light gets to the retina (the portion of the eye that initially processes visual information and delivers it to the brain).
The iris constricts when it’s bright out and opens up in lower light conditions. This is called the “pupillary light reflex.”
Disorders that affect the iris can occur due to genetic abnormalities or other conditions, such as glaucoma, Horner syndrome, Holmes-Adie syndrome, and more.
The iris is the part of the eye that makes up your eye color. A circular muscle with a hole in the middle, the iris contracts and expands to control the amount of light that gets into the pupil.
The iris sits in theuvealtract, which is the eye’s middle layer. It is made up of the following parts:
The iris sits in front of the lens within the coronal plane towards the front of the eye. Unbound in its middle to allow the pupil to change size, this structure is connected to the ciliary body—the part of the eye that produces the eye’s fluid (aqueous humor) and regulates contraction and constriction of the iris.
Anatomical Variations
The most common variation in iris anatomy is a condition calledaniridia, in which the iris is incomplete or absent. Usually affecting both eyes, this congenital (occurring at birth) defect can be the result of either injury or mutations to thePAX6gene.
Aniridia leads to a range of symptoms, including:
Eye Color
Brown eyes have a higher amount of melanin, while blue eyes have very little pigment. The amount of pigment is often related to a person’s genes, skin type, and hair color.
Via dilation (opening) and constriction (closing), the iris plays a key role in regulating the amount of light that accesses the retina in the back of the eye.
Checking the health of the irisas well as proper pupillary reflexes is an important part of vision care. Testing is needed to diagnose conditions and allows your healthcare provider to know if this part of the eye is functioning normally.
Eye specialists (ophthalmologists) and optometrists have several tests they can use, including:
If your provider needs to examine a specific condition, they may order some imaging tests, such as:
Summary
16 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.American Association for Pediatric Ophthalmology & Strabismus.Anisocoria and Horner’s syndrome.Medline Plus.Iris.Borrás T.The cellular and molecular biology of the iris, an overlooked tissue: the iris and pseudoexfoliation glaucoma.J Glaucoma. 2014;23(8 Suppl 1):S39-42. doi:10.1097/IJG.0000000000000104Medline Plus.Aniridia.Boyd K, Turbet D.Parts of the eye. American Academy of Ophthalmology.Bloom J, Motlagh M, Czyz CN.Anatomy, Head and Neck: Eye Iris Sphincter Muscle. [Updated 2023 Jul 30]. In: StatPearlsNational Library of Medicine.Oculocutaneous albinism and ocular albinism overview.Johns Hopkins Medicine.Glaucoma.National Institutes of Health.Congenital horner’s syndrome.National Organization of Rare Disorders.Essential iris atrophy.National Institutes of Health.Holmes-Adie syndrome.National Institutes of Health Genetics Home Reference.Coloboma.American Academy of Ophthalmology.Anterior segment trauma: Evaluation, considerations and initial management.National Eye Institute.Uveitis.Stanford Medicine.Pupillary responses.Broadway DC.How to test for a relative afferent pupillary defect (RAPD).Community Eye Health. 2012;25(79-80):58–59.
16 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.American Association for Pediatric Ophthalmology & Strabismus.Anisocoria and Horner’s syndrome.Medline Plus.Iris.Borrás T.The cellular and molecular biology of the iris, an overlooked tissue: the iris and pseudoexfoliation glaucoma.J Glaucoma. 2014;23(8 Suppl 1):S39-42. doi:10.1097/IJG.0000000000000104Medline Plus.Aniridia.Boyd K, Turbet D.Parts of the eye. American Academy of Ophthalmology.Bloom J, Motlagh M, Czyz CN.Anatomy, Head and Neck: Eye Iris Sphincter Muscle. [Updated 2023 Jul 30]. In: StatPearlsNational Library of Medicine.Oculocutaneous albinism and ocular albinism overview.Johns Hopkins Medicine.Glaucoma.National Institutes of Health.Congenital horner’s syndrome.National Organization of Rare Disorders.Essential iris atrophy.National Institutes of Health.Holmes-Adie syndrome.National Institutes of Health Genetics Home Reference.Coloboma.American Academy of Ophthalmology.Anterior segment trauma: Evaluation, considerations and initial management.National Eye Institute.Uveitis.Stanford Medicine.Pupillary responses.Broadway DC.How to test for a relative afferent pupillary defect (RAPD).Community Eye Health. 2012;25(79-80):58–59.
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.
American Association for Pediatric Ophthalmology & Strabismus.Anisocoria and Horner’s syndrome.Medline Plus.Iris.Borrás T.The cellular and molecular biology of the iris, an overlooked tissue: the iris and pseudoexfoliation glaucoma.J Glaucoma. 2014;23(8 Suppl 1):S39-42. doi:10.1097/IJG.0000000000000104Medline Plus.Aniridia.Boyd K, Turbet D.Parts of the eye. American Academy of Ophthalmology.Bloom J, Motlagh M, Czyz CN.Anatomy, Head and Neck: Eye Iris Sphincter Muscle. [Updated 2023 Jul 30]. In: StatPearlsNational Library of Medicine.Oculocutaneous albinism and ocular albinism overview.Johns Hopkins Medicine.Glaucoma.National Institutes of Health.Congenital horner’s syndrome.National Organization of Rare Disorders.Essential iris atrophy.National Institutes of Health.Holmes-Adie syndrome.National Institutes of Health Genetics Home Reference.Coloboma.American Academy of Ophthalmology.Anterior segment trauma: Evaluation, considerations and initial management.National Eye Institute.Uveitis.Stanford Medicine.Pupillary responses.Broadway DC.How to test for a relative afferent pupillary defect (RAPD).Community Eye Health. 2012;25(79-80):58–59.
American Association for Pediatric Ophthalmology & Strabismus.Anisocoria and Horner’s syndrome.
Medline Plus.Iris.
Borrás T.The cellular and molecular biology of the iris, an overlooked tissue: the iris and pseudoexfoliation glaucoma.J Glaucoma. 2014;23(8 Suppl 1):S39-42. doi:10.1097/IJG.0000000000000104
Medline Plus.Aniridia.
Boyd K, Turbet D.Parts of the eye. American Academy of Ophthalmology.
Bloom J, Motlagh M, Czyz CN.Anatomy, Head and Neck: Eye Iris Sphincter Muscle. [Updated 2023 Jul 30]. In: StatPearls
National Library of Medicine.Oculocutaneous albinism and ocular albinism overview.
Johns Hopkins Medicine.Glaucoma.
National Institutes of Health.Congenital horner’s syndrome.
National Organization of Rare Disorders.Essential iris atrophy.
National Institutes of Health.Holmes-Adie syndrome.
National Institutes of Health Genetics Home Reference.Coloboma.
American Academy of Ophthalmology.Anterior segment trauma: Evaluation, considerations and initial management.
National Eye Institute.Uveitis.
Stanford Medicine.Pupillary responses.
Broadway DC.How to test for a relative afferent pupillary defect (RAPD).Community Eye Health. 2012;25(79-80):58–59.
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