Our pupils’ fast response to light appears to occur even without input from the brain. For example, it is seen in people with damage to the visual cortex. Appearances can be deceptive, though.

Usually, your pupils dilate and constrict together and are the same size as each other. Unequal pupils happen when one pupil is not reacting to light as it should. If the iris muscle is paralyzed ...

Pupils are large in the dark to let more light in and small in bright light. Usually, the pupils in each eye dilate or constrict simultaneously. When they do not, the pupils may appear to be ...

Opioids usually make a person’s pupils constrict. This is when the black part at the center of the eye gets smaller, reducing the amount of light that gets inside. Typically, pupil constriction ...

Dilated pupils, or pupils that are larger than normal, have many causes. Injury, a medical condition, or drug use are a few causes of this condition. (Photo Credit: Moment/Getty Images) ...

Small, constricted pupils can be a side effect of opioid use. Learn about other signs to watch for and how to bring up your concerns in a helpful, compassionate way.

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 ...

Life Rats fooled by optical illusion may shed light on evolution of the eye. The Asahi illusion tricks us into believing it is brighter than it really is, to the extent that our pupils constrict.

Meet two women with unusual ways of experiencing the world: One cannot revisualize people or events, while the other may imagine too much.