The pupil is the small black circle in the centre of the iris. It is a tiny hole present over the lens through which light enters the eye and focuses on the retina for image formation. The iris muscles regulate the size of the pupil and control the amount of light entering it.
The pupil is black because all the light that goes inside gets absorbed by the retina. It is like an aperture of the camera. There are two types of iris muscles that control the size of the pupil. They are:
- Circular sphincter pupillae – constricts pupil on contraction
- Radial dilator pupillae – dilates pupil on contraction
This is called the pupillary light reflex, which controls the diameter of the pupil and controls the light intensity entering the pupil. It responds to the light striking ganglion cells present in the retina at the posterior part of the eye. The pupil dilates in dim light and constricts under bright light. This way it protects the lens and retina from damage from high light intensity and also allows us to see clearly under dim conditions.
The colour of the pupil becomes pale yellow when the lens becomes opaque or cloudy in case of cataract.
This was in brief about Pupil. Test your understanding with MCQs on Structure of Eye, only at BYJU’S.