Question

How does the eye regulate the amount of light that falls of on the retina? Answer briefly.

Answer 1

The iris is a circular muscular diaphragm containing the pigment giving eye its colour. It contains two types of smooth muscles, circular muscles (sphincters) and radial muscles (dilators), of ectodermal origin. The iris contains two sets of smooth muscles : circular (sphincter) and radial (dilator). In bright light, the circular or sphincter muscles contract. The pupil (aperture of iris) becomes narrow so that less light enters the eye. In dim light the radial or dilator muscles contract. Pupil becomes wide so that more light enters the eye.