Why do the pupils of our eyes change size?

问题：我们眼睛的瞳孔为何会改变大小？

回答：Because we have to adapt to environment of different light intensity.

因为我们需要适应不同光强度的环境。

In the middle of the iris is a round opening called the pupil, which looks like a black circle. The size of the pupil regulates the amount of light that enters the eye. Two muscles in the iris automatically adjust the size of the pupil to the level of the light. In dim light, the dilator muscle enlarges the pupil, so as much light as possible can then enter the eye. In bright light, the sphincter muscle makes the pupil smaller, which prevents too much light from entering the eye. The pupil also becomes smaller when the eye looks at the nearby object, thus bringing the image into sharp focus.

adjust the light changing.

suprise...