What and why do the pupils of human eyes react?

Scientists have long known that humans and other higher vertebrates have pupillary reaction... This is the name of the reflex in which the sizepupils change depending on the amount of light entering the eyes. If you believe the calculations, in bright light, the pupil narrows sharply in 5 seconds, and when a person or animal enters a dark space, it expands within 5 minutes. It is believed that this reflex is necessary for the protection of the organs of vision and the ability to see at different levels of illumination. Pupil size can also change for other reasons, such as sexual arousal, illness, and taking various medications. Recently, Australian scientists found that the diameter of the pupils also changes depending on how many objects are in the person's field of view. This discovery can help in the treatment of a rather serious illness.

People's pupils change with more than just light levels


  • 1 What causes the pupils to dilate?
    • 1.1 Taking medications
    • 1.2 Use of prohibited substances
    • 1.3 Head injuries
    • 1.4 Injury to the organs of vision
    • 1.5 Sexual attraction
  • 2 A new cause of pupil dilation

What causes the pupils to dilate?

Pupil sizes are controlled by the muscles of the irismembranes of the eyes. In bright light, they taper to prevent too much light from entering the eyes. And in the dark, they expand, because this way more light penetrates the organs of vision - this significantly improves the ability to see in low light. In bright light, the diameter of the pupils is 2 to 4 millimeters, and in the dark, they expand to 8 millimeters. As people age, the size of people's pupils decreases slightly.

Interesting fact: about 20% of the world's population has a disease anisocoria... With it, both pupils of a person react to light, but at the same time differ in diameter.

Normal pupils, dilated pupils, and pupils with anisocoria

In addition to reacting to light, there are other reasons why pupils change their size.

Taking medicines

Most often, medications affect the size of the pupils. This is a side effect of anti-allergy, edema, motion sickness and antidepressants.

Pupils may dilate due to medication

Use of prohibited substances

Dilated pupils can be observed in people who have consumed prohibited substances. The eye's reaction to color is caused by cocaine, LSD, and so on.

A person who uses illegal substances can literally be recognized by their eyes.

Head injury

You could surely have seen how when examiningdoctors shine a flashlight in his eyes of an injured athlete. In this way, they check if he has received brain damage - if so, the reaction of the pupils to light changes.

Altered pupil size may indicate a head injury

Eye injuries

In some cases, a person's pupils remain dilated due to damage to the iris. Most often, such injuries occur during complex cataract surgeries or corneal transplants.

Pupil size may change due to trauma to the iris

Sexual attraction

Scientists already know for sure that pupil dilationdirectly related to sexual interest. In the course of the experiment, they found that the pupillary reaction occurs when men or women look at attractive people. Unfortunately, the cause of this phenomenon has not yet been identified.

A person's pupils change when they see an attractive object.

See also: Why are eyes of different colors and which color is the rarest?

New cause of pupil dilation

Recently, Australian scientists found out that the sizepupils also change depending on how many objects the person is looking at. This was proven in an experiment in which several volunteers looked at an image with varying numbers of black and white dots. Some of them were connected with a line so that a dumbbell shape was formed. When people looked at the images, the researchers monitored the size of their pupils. It turned out that in the presence of a large number of points, they really expand. And when the volunteers saw few dots, the pupils before their eyes, on the contrary, became small.

When a person sees many objects, his pupils also dilate.

According to the authors of the scientific work, human visionassociated with its ability to perceive numerical information. In theory, if a person has problems understanding mathematics, the pupils will not respond to the number of objects in the field of view. If this is true, in the future, doctors will be able to monitor the reaction of the pupils to a different number of points and identify in children dyscalculia... This is the name of a person's inability to learn arithmetic. If you identify this problem early, you can help people avoid serious consequences.

Dyscalculia - a person's inability to learn mathematics

If you are interested in science and technology news, subscribe to our channel in Yandex.Zen. There you will find articles that have not been published on the site!

Finally, here's another interesting fact - in space, people begin to twitch their eyes. Read about why this happens in this material.