The iris (plural: irides or irises) is a thin, circular structure in the eye, responsible for controlling the diameter and size of the pupils and thus the amount of light reaching the retina. "Eye color" is the color of the iris, which in humans can be green, blue, or brown. In some cases it can be hazel (a combination of light brown, green and gold), grey, violet, or even pink. In response to the amount of light entering the eye, muscles attached to the iris expand or contract the aperture at the center of the iris, known as the pupil. The larger the pupil, the more light can enter.

The word iris is derived from the Greek goddess of the rainbow, due to the many colours of the iris.

The iris develops from the anterior two layers of an embryonic neuroectoderm structure called the optic cup. The optic cup also produces the iris sphincter and dilator muscles.

The iris consists of two layers: the front pigmented fibrovascular tissue known as a stroma and, beneath the stroma, pigmented epithelial cells.

Iris commonly refers to:

Iris may also refer to:

Anatomy (from the Ancient Greek ἀνατέμνειν, anatemnein: ana, "separate, apart from", and temnein, "to cut up, cut open") is a branch of biology and medicine that is the consideration of the structure of living things. It is a general term that includes human anatomy, animal anatomy (zootomy), and plant anatomy (phytotomy). In some of its facets anatomy is closely related to embryology, comparative anatomy and comparative embryology, through common roots in evolution.

Anatomy is subdivided into gross anatomy (or macroscopic anatomy) and microscopic anatomy.Gross anatomy is the study of anatomical structures that can, when suitably presented or dissected, be seen by unaided vision with the naked eye.Microscopic anatomy is the study of minute anatomical structures on a microscopic scale. It includes histology (the study of tissues), and cytology (the study of cells). The terms microanatomy and histology are also sometimes used synonymously (in which case the distinction between histology and cell biology isn't strictly made as described here).