Do pupils dilate in the dark?

To control the amount of light entering the eye, the iris widens or narrows to change the size of the pupil. For example, when it's dark, the iris widens and the pupil dilates, or gets bigger, to allow as much light as possible to enter the eye. The opposite occurs during the day. read more

Short of chemical interventions—such as the eyedrops ophthalmologists use to widen their patients' pupils for eye exams—the only way to dilate or shrink the pupils is by changing the amount of available light. Switch off the lamp, and your pupils will widen to take in more light. Step out into the sun, and your pupils will narrow. read more

Your pupils can also constrict and dilate as a result of a variety of medicines and drugs. In fact, doctors will often shine a light into a patient's eyes to test the reaction of the pupil to determine whether the body appears to be functioning properly. read more

In low light, your pupils open up, or dilate, to let in more light. When it’s bright, they get smaller, or constrict, to let in less light. Sometimes your pupils can dilate without any change in the light. read more