Question

State one function of iris in human eye.

Answer 1

 Hint: Eyes are the pair of globular organs of sight present in the head of humans and other vertebrates. In humans and most mammals and birds a thin, annular structure is present in the eye called iris. They are called the diaphragm for the pupil.

Complete Step by Step Answer:
The Iris of the eye is a thin, annular structure. They are mainly responsible for controlling the size and diameter of the aperture called the pupil. This adjusts the amount of light that reaches the retina and helps in adjusting the vision according to the surrounding lighting conditions.
When there is an ample amount of light in the surrounding, the pupil shrinks to allow less light into the retina and in dark conditions, the pupils dilate to allow the maximum amount of light to fall on the retina. This helps in forming a clear and well- lit image on the retina and thus we can see clearly.
This is done with the help of sphincter pupillae muscles which pull the iris radially to enlarge or relax to contract the pupil.
- Iris is usually a strongly pigmented structure and it imparts the colours to the eye. The colours usually vary as brown, hazel, green, blue, and gray. In some cases such as occulo- cutaneous albinism, there is a lack of pigmentation and the eye may be pinkish- white in colour.
- Irrespective of the colour, the only pigment that contributes to the human iris colour is the melanin.

Note: Iridoplegia is the paralysis of the sphincter muscles that can cause the loss of contraction of the pupil and even loss of accommodation reflex.