Iris

The iris is a colorful, often intricate structure found in the eyes of humans and many animals, playing a crucial role in regulating the diameter and size of the pupil and thus the amount of light reaching the retina. The iris is located between the cornea and the lens, and its color can vary widely among individuals, ranging from brown and hazel to green, blue, and gray. In Hebrew, the iris is called הווער (ha'iriss), while in Spanish it is known as iris, in French as iris, in German as Regenbogenhaut, and in Japanese as 虹彩 (kōsai). The iris is composed of two layers: the stroma, which contains connective tissue, blood vessels, and pigment cells, and the iris pigment epithelium, which is a layer of cells that produce melanin, the pigment responsible for eye color. The iris's ability to control pupil size is achieved through the contraction and relaxation of two sets of muscles: the sphincter pupillae and the dilator pupillae. This mechanism is essential for maintaining optimal light levels for vision and protecting the retina from excessive light exposure.