Miosis is the constriction of the pupil in the eye, which reduces the amount of light that enters. This process is controlled by the iris, the colored part of the eye, and is often a response to bright light or certain medications. Miosis can help protect the retina from excessive light exposure. In addition to light exposure, miosis can occur due to various factors, including narcotics, certain neurological conditions, or as a side effect of some medications. It is the opposite of mydriasis, which is the dilation of the pupil. Understanding miosis is important in assessing eye health and neurological function.