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Have you ever looked in the mirror to see if your pupils get bigger or smaller in the dark? Maybe you’ve noticed a change in your friends’ eyes late at night. Do you know why your pupils change size? Is it dangerous? Is it something you should be worried about? Let’s find out!

Why Pupils Get Bigger in the Dark


While we are talking about pupils, let’s first start with the iris (the colored part of your eye). The iris’ main job is to limit the amount of light that enters the eye through your pupil (the black, center part of your eye). 

Your eyes need just the right amount of light to see properly. When it is light outside, or you have bright lights on in your home or office, the pupils in your eyes will appear smaller because they don’t need to bring in quite so much light. Do pupils get bigger in the dark? Yes! When your environment is darker, your pupil will look bigger (dilated) in size because it needs to let in more light for you to be able to see the best you can. 

Although it seems like your pupil is contracting and changing size, it is the iris that is widening or narrowing to adjust the pupil size. Kind of cool, right?

Why Pupils Might Not Enlarge in the Dark


While your eyes are constantly changing size with the change of light throughout the day, if your answer to the question “do pupils get bigger in the dark?” is “no, they don’t dilate or get larger when it is dark,” you have a condition called abnormal miosis. 

Abnormal miosis can be a result of age or the muscles that control your pupils getting weak. It can also be a side effect from medication or from an eye injury that is inflamed and swollen. 

Congenital miosis is when you possess a gene that makes it so that your pupils don’t dilate. Horner’s syndrome is relatively rare but can also affect your eyes not being able to dilate because your brain isn’t properly communicating to both your eyes. Even a very severe lack of vitamin D could be the cause.

Can Pupils Enlarge in the Day?


There can be many reasons for people’s eyes dilating and getting bigger during the day. They may include:

  • Medications 
  • Eye injuries
  • Brain injury or disease
  • Sexual attraction

When It’s Time to See an Eye Specialist

If you notice a change in your eyes, especially if it’s sudden and is accompanied by other symptoms of a stroke or eye injury, go to the emergency room immediately to receive treatment.

If you suspect other changes are happening with your eyes and vision or just have questions, the eye specialists at Vision Boutique would love to talk to you about your concerns. Schedule an eye exam and learn more about your eyes and how to keep your and your family’s vision a top priority.

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