Eye See What You Did There: A Pupil’s Response to Light

Many believe that eyes are the window to the soul. Some believe that the color of your eyes dictates your personality. However, what about your pupils? Are they part of the window, showing others what lies within your mind?

A Pupil's Response to Light

What are pupils?

A PUPIL is the black center part of your eye. It helps bring in light and focus on objects around you so you can see (read: The Guide for Assessing PERRLA). Your eye also has muscles residing in the iris. This controls the pupil.

Another way to naturally control your pupil is thinking about light or darkness. Whether if you’re thinking about a bright sunny day or the pitch-black ocean waters, you will control your pupil’s constrict or dilate functions.

How do they respond to light?

Pupils respond quickly to light. Different hues and the direction of the light itself will determine how quickly your pupils will constrict or shrink.

For example, imagine walking outside when the sun is sitting at high noon. Your eyes will adjust from being indoors to the natural light outside. The speed of your pupil will shift around .097 mm/second under constriction.

Transitioning from natural light to indoors, especially if it’s dim or dark, your pupils will dilate and readjust to their surroundings. It will take longer for your pupils to adjust in the dark due to light absorption in your eyes. In general, consider your eyes fully adjusted between 20 to 40 minutes.

How to check pupils with a penlight?

Many of us remain curious about the different responses from our bodies. From lifting weights to monitoring average screen time to maintain appropriate eye health varies with each person.

Checking one’s pupils isn’t challenging, as long as it’s done correctly and safely. One common way to check your pupils is using a penlight.

Majority of doctors use the penlight method to test your pupil’s reactions and reflexes to light. This is achieved once you hold the penlight about 20 inches away from your eyes. Aim directly in each eye to receive the full effect of the constriction and/or dilation.

Respon pupil with penlight

After several seconds, remove the light and begin testing the accommodation with one finger four inches away from the nose. This is making sure the pupils can restrict on cue (or close to it).

Concerning responses regarding your pupils.

Normally, pupils should react accordingly. If your pupils react slower than usual, then you may deal with Adie syndrome. ADIE SYNDROME is a rare neurological disorder that affects the pupil in your eye. This could sometimes display larger than usual in addition to the sluggish reaction to direct light.


Pupil response to light is important for your eye health. Your eyes may show signs of stress, inflammation, or other concerning symptoms if the pupil dilates or constrict slower than anticipated (or not at all).

Take time to rest and relax your eyes. Avoid direct light in your eyes so your pupil response to light stays on point.

Finally, consume an eye-healthy diet to enhance your vision. Proper nutrients and rest promote excellent eye health and stronger vision.