The pupillary response refers to the way the pupils of the eyes adjust in size in reaction to light and other stimuli. When exposed to bright light, the pupils constrict to limit the amount of light entering the eye, protecting the retina. Conversely, in low light conditions, the pupils dilate to allow more light in, enhancing visibility. This response is controlled by the autonomic nervous system, specifically the iris sphincter muscle and the dilator muscle. The pupillary response can also indicate certain health conditions, as abnormal reactions may suggest issues with the nervous system or eye health.