MedBucket

Iris is a part of the middle layer of the eye. It has its anterior and a posterior side, a border  and an opening called pupilla (pupil).

The anterior side of iris (facies anterior iridis) is free, slightly convex because of the lens which is located behind it. Where the two lateral and one medial third meet, there is a ledge called iridal ledge. The iridial ledge divids iris into two parts — the bigger called anulus irids major and a smaller called anulus iridis minor. On the bigger one there are circular creases, while the smaller one contains cavities. The cavities are called the iridial crypts.

The posterior side of iris is slightly concave and is touching the frontal side of the lens. These two aren’t glued to one another — they are just rubbing onto each other, thus allowing the eye water to pass from the camera bulbi posterior to the camera bulbi anterior. There are pathological cases when these two structures get glued to one another, and that is called the secclusio pupillae. This can cause permanent blindness if not operated immediately.

Iris is made out of binder tissue and smooth muscle fibers. It is comprised of four layers:

1. Endothelium camerae anterioris
2. Stroma
3. Stratum musculare
4. the iridial part of the inner layer of the eye

1. This layer is actually covering the stroma on the front side. It is only present in children — later it gets ruptured and disappears.

2. This layer is the main part of iris. It is made out of binder tissue filled with pigment and non-pigment cells. The presence or non-presence of pigment cells in this layer determins the color of people’s eyes. People who have a lot of pigment cells in this layer have black or brown eyes. People who have small amounts of pigment cells have green eyes. People who have very small amounts of pigment cells in this layer have blue eyes. Finally, people who don’t have any pigment cells in this layer have specific dark-blue eyes.

3. This layer consists of two muscles: musculus sphincter pupillae and musculus dilatator pupillae. This first one tightens the pupil, while the second one relaxes it.

4. This layer origins from the brain, and is made out of 3-4 layers of epithelial cells.

The innervation origins from the plexus ganglious ciliaris — its branches head towards the pupil and produce the plexus pupillaris around it.