What is the impact of light intensity on pupil size?

Light intensity directly impacts pupil size, with brighter light causing the pupils to constrict and dimmer light causing dilation.

The human eye is a complex organ that has evolved to function optimally in a wide range of light conditions. One of the ways it achieves this is through the adjustment of pupil size in response to changes in light intensity. The pupil is the black circular opening in the centre of the iris, which controls the amount of light that enters the eye.

When the light intensity is high, such as in bright sunlight, the pupils constrict or become smaller. This is known as miosis. The constriction of the pupils in bright light conditions reduces the amount of light entering the eye, protecting the sensitive retina from potential damage due to overexposure.

Conversely, when the light intensity is low, such as in a dimly lit room or at night, the pupils dilate or become larger. This is known as mydriasis. The dilation of the pupils in low light conditions increases the amount of light entering the eye, enhancing visibility in the dark.

The process of pupil dilation and constriction is controlled by the autonomic nervous system. The sphincter pupillae muscle, stimulated by the parasympathetic nervous system, constricts the pupil in response to bright light. On the other hand, the dilator pupillae muscle, stimulated by the sympathetic nervous system, dilates the pupil in response to low light.

In summary, the size of the pupil is directly influenced by the intensity of light in the environment. This automatic adjustment helps to optimise vision under different lighting conditions and protect the eye from potential damage.