In this article, we will go over the anatomy of the iris and the drainage angle.
From anterior (front) to posterior (back), the layers of the iris are:
The stroma consists of a pigmented fibrovascular tissue which connects to both the sphincter muscles ****that constrict the pupil, and the dilator muscles which pull on the iris radially to enlarge the pupil. The most posterior surface of the iris is lined by the iris pigment epithelium - a layer which is around 2 cells thick. On the contrary, the anterior surface of the iris has no epithelium.
The outer edge of the iris is known as the root, and is attached to the sclera and the anterior ciliary body. Together, the iris and the ciliary body make up the anterior uvea. Directly infront of the root of the iris is the “angle” of the eye - where the iris meets the sclera. This structure is clinically important as it is the main pathway through which aqueous humour drains out of the eye, and therefore diseases of the iris may result in effects on intraocular pressure and vision. Check out our glaucoma article!
The iris is divided into the inner pupillary zone (so called as it forms the boundary of the pupil) and outer ciliary zone (which extends all the way to the ciliary body), separated by the collarette. The collarette is also the area where the sphincter muscle and dilator muscles overlap.