Pupil Dilation Experiment (to do at Home with Kids)

Pupil Dilation Experiment (to do at Home with Kids)

Inside: a pupil dilation experiment you can do at home with kids. It’s a hands-on way to discover how quickly our eyes adjust to a variety of light conditions. 

Do your kids have an eye exam coming up? Is it going to involve pupil dilation to examine the back of the eye?


We recently took our 9-year-old for just such an exam, and it was a very traumatic experience for all involved. To prep for the day, we read the Eye book by David Macaulay and explained to our son that as part of the exam, the ophthalmologist will place eye drops in each eye to widen the pupil. That will allow more light in so the doctor can see inside the eye.


Pupil Dilation Experiment for Kids #science #humaneye #homeschooling #earlychildhoodeducation


My son, who is usually very reasonable and easy going, absolutely refused to have the doctor place drops in his second eye because (according to him) his first eye was burned by the drops.


We reasoned. We bribed. We threatened. The doctor was getting very annoyed. The waiting room area was getting very noisy as we were holding up the traffic. But my son just got stuck in the “no way I’m doing this” mode.


You’re probably wondering, why didn’t you just leave, let him snap out of it, and return on another day? It’s hard to believe, but pediatric ophthalmologists in Chicago are booked a year in advance. If we had walked out of that appointment, we would have had to wait another year to return.




When we couldn’t wait any longer, we used force. A receptionist, a nurse, and my husband held down my 9-year old while the doctor advanced with the eye drops at the ready. In the ensuing scuffle, the drops made their way on every surface in the room. I’m surprised we all didn’t walk out of there with dilated pupils. It was a battle of epic proportion.


When it was over, we were all mighty relieved. And the inside of my son’s eyes were just fine, thanks for asking.


As soon as he was calm, we talked about the experience, hugged, and further connected by reading aloud a Star War book that my son likes. When he went to play with his siblings, I started planning an Eye Dilution experiment. Since we fear things that don’t make sense to us, I believe the more that we know and understand, the less we fear.


Whether you have an eye exam coming up or not, you might enjoy trying this pupil dilation experiment with your kids.




Pupil Dilation Experiment


Let’s have a look at the pupil with a doctor’s eye.



  • Magnifying glass
  • Handheld mirror
  • Flashlight (we used a phone flashlight)

Pupil Dilation Experiment for Kids #science #humaneye #homeschooling #earlychildhoodeducation




  1. The parent places the magnifying glass on the mirror and holds it up for a kid (with the magnifying glass facing the child). Ask your kid to look into the center of the magnifying glass. He/she might need to move his/her head around to get a good image of one eye at a time.  Older kids can hold the mirror and magnifying glass on their own. 


Ask kids to look at:

  • the white of the eye,
  • the colored part of the eye, or iris,
  • the black hole in the middle of the iris, the pupil.

Pupil Dilation Experiment for Kids #science #humaneye #homeschooling #earlychildhoodeducation

  1. Hold a flashlight with your other hand, place it behind the mirror, and shine the light around the edge of the mirror into your child’s eye.



Can you see your pupil change size?

Pupil Dilation Experiment for Kids #science #humaneye #homeschooling #earlychildhoodeducation

  1. Go to a dimly lit room (bathroom, perhaps) and repeat step 1. If you don’t have a night light, use a candle or a flashlight that is turned away from you so it’s not too bright.



Did you notice that it takes longer for the pupil to dilate than to contract?

Pupil Dilation Experiment for Kids #science #humaneye #homeschooling #earlychildhoodeducation

Repeat the same with the other eye.



Here are some of the questions that came up during our experiment.


How do we see things?


The pupil is a hole in the center of the iris, the colored part of the eye. Through this hole, the light travels to the back of the eye. The light then is coded into a nerve signal that travels to the brain. Your brain decodes the message and interprets it.


What does the pupil size have to do with it?


The iris regulates how much light gets into the eye. Pupils are smaller in bright light and larger in low light. Your pupils also expand when you are nervous (if you see a bear) and when your brain is working on a very hard math problem (the harder the problem, the bigger the pupil). 


Why the drops?


To see well inside your eye your eye doctor needs to use a very bright light. This bright light causes the pupils to constrict. A doctor uses medicated eye drops to immobilize this light reflex. The pupils stay wide open even when a doctor is shining a bright light into the eyes to illuminates the back of the eye. 


Can a flashlight hurt my eyes?

According to the American Academy of Ophthalmology, a typical flashlight cannot hurt your eyes.  Iris, retina, pupil and optic nerve all work together to activate our build in defense ability to protect our eyes from the glare of the bright light. The first impulse is to blink (to shut the eyes from the glare) and by the time the blink is over the pupils are constricted. But don’t go around doing it for fun! 


Books that helped our Eye investigation 


The Eye Book by Dr. Seuss

Eye to Eye: How Animals See the World by Steve Jenkins

Where Did You Get The Color of Your Eyes by Baby Professor

How Can My Eyes See? Biology 1st Grady by Baby Professor 

The Doctor with an Eye for Eyes: The Story of Dr. Patricia Bath by Julia Finley Mosca

The Human Eye: A Fascinating Book Containing Human Eye Facts, Trivia, etc. by Matthew Harper

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All my kids ended up participating in this experiment and we had a lot of fun! I personally never looked at my eyes with a magnifying glass before and I found the whole experience fascinating. I was as excited as kids to run between the flashlight and the dark room. It was a truly hands-on way to discover how quickly our eyes adjust to a variety of light conditions. 

Looking for more Science Ideas? Check out Kid Minds Science


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