n, pl  iris*es  or  iri*des   1  :  the opaque muscular contractile diaphragm that is suspended in the aqueous humor in front of the lens of the eye, is perforated by the pupil and is continuous peripherally with the ciliary body, has a deeply pigmented posterior surface which excludes the entrance of light except through the pupil and a colored anterior surface which determines the color of the eyes  2  :  IRIS DIAPHRAGM .
 
 
 
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