iris
(ī′rĭs)
To hear audio pronunciation of this topic, purchase a subscription or log in.
(ī′rĭ-dēz″)
(ir′ĭ-dēz″)
pl. irides [Gr. iris, stem irid-, the goddess Iris, the messenger of the Olympian gods; rainbow; iris (plant)]
The opaque, pigmented continuation of the choroid layer of the eye that partly covers the lens, surrounding the pupil and regulating the amount of light that strikes the retina. The iris lies in the aqueous compartment of the eye. It divides the posterior chamber of the aqueous compartment (into which aqueous fluid is secreted) and the anterior chamber (from which aqueous fluid is absorbed). Muscles in the iris can expand or contract the pupil.
SEE: aniridia; SEE: choroidoiritis; SEE: heterochromia iridis; SEE: rubeosis iridis
ANATOMY
The front surface of the iris is irregular and covered with grooves and ridges. The posterior surface contains radially oriented myofilaments, which together form the dilator pupillae muscle (which widens the pupil in response to sympathetic stimulation). A separate set of concentric myofilaments forming circles around the pupil compose the sphincter pupillae muscle (which narrows the pupil in response to parasympathetic stimulation). The color of the iris is determined by the concentration of melanocytes: if there are few cells, the color will be blue; increasing concentrations of melanocytes lead to darkening color on a spectrum from greenish-blue, to gray, to brown.
There's more to see -- the rest of this topic is available only to subscribers.
Citation
Venes, Donald, editor. "Iris." Taber's Medical Dictionary, 24th ed., F.A. Davis Company, 2021. Nursing Central, nursing.unboundmedicine.com/nursingcentral/view/Tabers-Dictionary/752593/all/iris.
Iris. In: Venes DD, ed. Taber's Medical Dictionary. F.A. Davis Company; 2021. https://nursing.unboundmedicine.com/nursingcentral/view/Tabers-Dictionary/752593/all/iris. Accessed November 1, 2024.
Iris. (2021). In Venes, D. (Ed.), Taber's Medical Dictionary (24th ed.). F.A. Davis Company. https://nursing.unboundmedicine.com/nursingcentral/view/Tabers-Dictionary/752593/all/iris
Iris [Internet]. In: Venes DD, editors. Taber's Medical Dictionary. F.A. Davis Company; 2021. [cited 2024 November 01]. Available from: https://nursing.unboundmedicine.com/nursingcentral/view/Tabers-Dictionary/752593/all/iris.
* Article titles in AMA citation format should be in sentence-case
TY - ELEC
T1 - iris
ID - 752593
ED - Venes,Donald,
BT - Taber's Medical Dictionary
UR - https://nursing.unboundmedicine.com/nursingcentral/view/Tabers-Dictionary/752593/all/iris
PB - F.A. Davis Company
ET - 24
DB - Nursing Central
DP - Unbound Medicine
ER -