How does the eye regulate the amount of light that falls on the retina

Explanation

Light reflected from an object enters the eye through the pupil. Iris controls the amount of light passing through by controlling the size of the pupil. Iris has two sets of smooth muscles which are arranged circularly and radially around the pupil. In dim light, the circular muscles of iris relax, whereas in bright light, they contract. On the contrary, in dim light, radial muscles contract and in bright light relax. Pupil regulates the amount of light passing into the eye. In bright light, it contracts and in dim light, it dilates so that the optimum amount of light required for proper vision reaches the retina.