What does the size of your pupils mean?

As you'll have noticed, the same pupil response can mean different things, although generally dilated pupils send a positive message and when they constrict it's a negative one. But exactly what it means depends on the situation (and whether someone has turned on a light).
A.

Who controls pupils size?

Light enters the eye through the pupil, and the iris regulates the amount of light by controlling the size of the pupil. The iris contains two groups of smooth muscles; a circular group called the sphincter pupillae, and a radial group called the dilator pupillae.
  • Why is the pupil black?

    The pupil is a hole located in the center of the iris of the eye that allows light to strike the retina. It appears black because light rays entering the pupil are either absorbed by the tissues inside the eye directly, or absorbed after diffuse reflections within the eye that mostly miss exiting the narrow pupil.
  • What does it mean if you have two different sized pupils?

    Normally the size of the pupil is the same in each eye, with both eyes dilating or constricting together. The term anisocoria refers to pupils that are different sizes at the same time. The presence of anisocoria can be normal (physiologic), or it can be a sign of an underlying medical condition.
  • How do your pupils dilate?

    Muscles in the colored part of your eye, called the iris, control your pupil size. In low light, your pupils open up, or dilate, to let in more light. When it's bright, they get smaller, or constrict, to let in less light. Sometimes your pupils can dilate without any change in the light.

Updated: 17th October 2019

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