A function of the body that happens automatically without a thought, was considered to be impossible to replicate at will. Yet a 23-year-old student in Germany can shrink and enlarge his pupils on ...

Medically reviewed by Johnstone M. Kim, MD Key Takeaways The pupil controls how much light enters the eye, allowing for clear ...

Opioids can cause small pupils, but so can several other things. If you’re concerned that someone is misusing opioids, there are other signs to look for. Share on Pinterest Chelsea Victoria/Stocksy ...

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 ...

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 ...

Anisocoria is when the pupils of your eyes are different sizes. Sometimes, unequal pupils can be a sign of health issues like multiple sclerosis or nerve damage. Medications placed in the eyes can ...