Question

Which part of the eye has the same name as the Greek goddess of the rainbow.

Answer 1

The iris is a circular muscular diaphragm containing the pigment giving eye its colour. That is why it has the same name as the Greek goddess of the rainbow. Iris separates the aqueous humour region into anterior and posterior chambers. It extends from the ciliary body across the eyeball in front of the lens. It has an opening in the centre called the pupil. It contains two types of smooth muscles, circular muscles (sphincters) and radial muscles (dilators), of ectodermal origin. The iris controls the amount of light entering the eye by the radial muscles contracting in dim light and the circular muscles contracting in the bright light. Both of these sets of muscles are under the control of the autonomic nervous system. Sympathetic stimulation causes the radial muscles to contract and the pupil to dilate, or get larger. Parasympathetic stimulation causes the circular muscles to contract and the pupil to constrict.