NCI Dictionary of Cancer Terms

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The NCI Dictionary of Cancer Terms features 7,791 terms related to cancer and medicine.

Browse the dictionary by selecting a letter of the alphabet or by entering a cancer-related word or phrase in the search box.

iris
(I-ris)
The colored tissue at the front of the eye that contains the pupil in the center. The iris helps control the size of the pupil to let more or less light into the eye.

EnlargeEye anatomy; two-panel drawing shows the outside and inside of the eye. The top panel shows outside of the eye including the eyelid, pupil, sclera, and iris; the bottom panel shows inside of the eye including the cornea, lens, ciliary body, retina, choroid, optic nerve, and vitreous humor.

Anatomy of the eye, showing the outside and inside of the eye including the eyelid, pupil, sclera, iris, cornea, lens, ciliary body, retina, choroid, vitreous humor, and optic nerve.