Question

What function does iris do while we are sleeping?

Answer 1

Iris is the dark muscular diaphragm, which controls the size of the pupil. It is coloured and it is responsible for controlling the amount of light reaching the retina by regulating the size of the pupil. The size of the pupil can fluctuate as the iris has tiny muscles that can either widen or narrow, depending upon surrounding light. At night, for example, the muscles will widen the pupil so there is sufficient light in the eye. When it is too bright outside, the pupil will contract to allow less light into the eyes and prevent damaging the retina.

When we sleep, our parasympatic system kicks in. Our blood pressure and heart rate decline, and our pupils become smaller (miosis) because they will not need to see anything because they will be closed for a long period of time.