![pupil plural eye pupil plural eye](https://www.2020mag.com/courses/120767/img1.jpg)
![pupil plural eye pupil plural eye](https://upload.wikimedia.org/wikipedia/commons/thumb/1/1e/Schematic_diagram_of_the_human_eye_en.svg/2000px-Schematic_diagram_of_the_human_eye_en.svg.png)
It is typically defined as the region where the sphincter muscle and dilator muscle overlap.įrom anterior (front) to posterior (back), the layers of the iris are: The collarette is the region of the iris separating the pupillary portion from the ciliary portion. The ciliary zone is the rest of the iris that extends to its origin at the ciliary body.The pupillary zone is the inner region whose edge forms the boundary of the pupil.The iris is divided into two major regions: Just in front of the root of the iris is the region through which the aqueous humour constantly drains out of the eye, with the result that diseases of the iris often have important effects on intraocular pressure, and indirectly on vision. The iris and ciliary body together are known as the anterior uvea. The outer edge of the iris, known as the root, is attached to the sclera and the anterior ciliary body. The back surface is covered by an epithelial layer two cells thick (the iris pigment epithelium), but the front surface has no epithelium. The stroma connects a sphincter muscle ( sphincter pupillae), which contracts the pupil, and a set of dilator muscles ( dilator pupillae) which open it. The iris consists of pigmented fibrovascular tissue known as a stroma. The word comes from Greek mythology, in which Iris is the anthropomorphized form of the rainbow. The following describes the iris of vertebrates, not the independently evolved iris found in some cephalopods. In anatomy, the iris (plural irises or irides) is the most visible part of the eye of vertebrates, including humans. 4.1 Genetic and physical factors determining iris colour.