The iris is a thin, annular structure in the eye responsible for controlling the diameter and size of the pupil, and thus the amount of light reaching the retina
. It is located in front of the lens and behind the cornea, and is bathed in front and behind by a fluid known as the aqueous humor
. The iris consists of two sheets of smooth muscle with contrary actions: the sphincter muscle, which constricts the pupil in bright light, and the dilator muscle, which expands the opening when it contracts
. The amount of pigment contained in the iris determines eye color, with very little pigment resulting in blue eyes and increased pigment leading to deep brown to black eyes
. Key features of the iris include:
- Muscles : The iris is made of muscles and nerves that work on their own without conscious thought
- Pigment : The color of the iris is unique to each individual, and it is determined by the amount of melanin (a naturally occurring pigment) produced by the body
- Aqueous Humor : The iris is filled with a fluid called aqueous humor, which helps maintain its shape and is constantly produced and drained by the eye
The iris can be affected by various conditions that affect the eyes, including inflammation (iritis or anterior uveitis), which can cause the iris to stick to the lens or the cornea, blocking the normal flow of fluid in the eye
. Inflammation can lead to secondary glaucoma and blindness, and treatment usually involves topical steroid eye drops
