What is the function of the pupil, and why does it change size? - #14662

The pupil is the black part of your eye that controls how much light enters, allowing you to see clearly in different lighting conditions. The iris, the colored part of your eye, controls the size of the pupil by expanding or contracting, which regulates the amount of light that reaches the retina. How the Pupil Works: In Bright Light: The pupil contracts (becomes smaller) to limit the amount of light entering and prevent damage to the retina. In Low Light: The pupil dilates (becomes larger) to allow more light in, helping you see better in dim conditions. This is called the pupillary light reflex and is controlled by the autonomic nervous system. Other Factors Affecting Pupil Size: Emotions: Strong emotions like excitement, fear, or stress can trigger pupil dilation (the "fight or flight" response). Medications: Certain drugs, like stimulants (e.g., caffeine, cocaine) or medications for eye conditions, can also cause pupil dilation or constriction. Focus: When you focus on something close, your pupils will constrict (this is called the near reflex). Abnormal Pupil Size: Uneven Pupil Size (Anisocoria): If one pupil is noticeably larger or smaller than the other, it might indicate a nerve issue or eye injury. Conditions like brain injury, nerve damage, or neurological disorders can affect how the pupils react. Dilated Pupil: Can be caused by drugs, trauma, or conditions like Adie’s tonic pupil or brain injury. Constricted Pupil: Can be a result of exposure to certain drugs or conditions like Horner's syndrome. When to Seek Medical Help: If you notice significant changes in pupil size or the reaction is no longer in sync with the surrounding light, it’s a good idea to seek medical attention. For example, if your pupils don’t constrict in bright light or if they suddenly become abnormally dilated for no reason, it could be a sign of a health concern.