Iris is present in the anterior part of the eye lens. It regulates the amount of light entering the eye. It is the visible part of the eye. It is pigmented and opaque. Iris’s muscles control the size of the aperture, which is known as the pupil. When the light is bright the iris closes the pupil and lets less light enter the eyes and when the light is dim it opens up the pupil more to allow more light to enter the eye.
It is present behind the cornea and above the eye lens. It originates from the ciliary body. The thick anterior portion of the choroid layer of the eye, which is known as the ciliary body extends further forming iris. It is a pigmented structure and the colour depends on the amount and nature of the pigment present in it, e.g. brown, grey, green, blue, etc. The quantity of melanin pigment determines the colour of the iris.
The iris is made up of two layers:
- Stroma – the front pigmented fibrovascular layer
- Pigmented epithelial cells – present at the back
The iris surrounds a small aperture called the pupil. The iris contains two sets of muscles. When the circular muscles contract, the size of the pupil decreases and when the radially arranged muscles contract the size of the pupil increases. This is how it works as a diaphragm controlling the size of the aperture and regulates the amount of light entering the pupil. This is under involuntary control.
This was in brief about Iris. Test your understanding with MCQs on Structure of Eye, only at BYJU’S.