Add Yahoo as a preferred source to see more of our stories on Google. Pupils often dilate in response to low light. Radu Bighian/Getty Images Dilated pupils mean that your pupils appear larger in size ...

The iris is a structure behind the transparent cornea of the eye. It has a circular opening called the pupil that changes size in response to the light level. Your pupils are usually the same size as ...

The pupil controls how much light enters the eye, allowing for clear vision. In low light, pupils widen to let in more light, and in bright light, they narrow to prevent too much light from entering.

New pupillometry research reveals how post-traumatic stress disorder (PTSD) may affect both branches of the autonomic nervous system. By measuring how someone's pupils dilate and constrict in response ...

Our pupils are a mirror of our state of arousal: they dilate when we are tense, stressed or even panicky, and constrict when we calm down. Key to this is an area of the brain measuring about 15 ...

Movie demonstrating the increase in accommodative eye vergence and pupil constriction when the fixating eye (left side of image, right eye of subject) is exposed to -5D defocus. The occluded eye ...

The eyes are a window into our autonomic nervous system. Everyone's unique personal history and autobiographical experiences have the power to influence how and when the sympathetic nervous system ...

Movie demonstrating the increase in accommodative eye vergence and pupil constriction when the fixating eye (left side of image, right eye of subject) is exposed to -5D defocus. The occluded eye ...

The size of your pupils can say a lot about your health and your state of mind. In most cases, pupils change size based on the light and dilate, meaning that appear larger, when you're in a darker ...