The pupils are black, round holes in the centre of the eyes that allow light to reach the optic nerve. The pupils become larger and smaller depending on how much light is coming in. Dilation is controlled by the coloured ring, the iris, which is made up of contracting and expanding muscle tissue. Incidence of light is not the only cause of enlarged pupils.

 

Possible causes for pupil dilation

1. light

The main reason for enlarging the pupils is to increase the ability to see in low light. In bright light, the pupils are very small because the maximum amount of light has been reached. In a dark room, the pupils dilate to allow more light to enter the eye so that the brain can interpret a better image. When there is a rapid change between light and dark, the pupils take a few seconds to adjust to the light conditions, so a normally lit room seems dark when you step into it from bright sunlight. Conversely, if you step out of the dark directly into the bright, you feel dazzled because for a moment too much light enters your eyes.

 

2. emotional and sexual arousal

The central nervous system controls the muscles of the iris, so the iris reacts to different emotional stimulation by contracting or dilating the pupils. So when sexually excited or looking at an attractive person, the pupils can dilate.

 

3. drugs

Certain drugs, both legal and illegal, can cause pupil dilation. Hallucinogenic drugs such as LSD, as well as other substances such as cocaine, marijuana, ecstasy and speed, act on the central nervous system (see above) to cause pupil dilation. Some prescription antidepressants are also known to dilate the pupils.

 

4. mydriatic

Mydriatics are medical eye drops that dilate the pupils. The ophthalmologist usually administers these eye drops in order to better examine and test the eyes and their reaction to light incidence. Since medical eye drops artificially dilate the pupils, you usually have to wear sunglasses for about an hour afterwards until your eyes return to normal. If the dilated pupils are exposed to too much light, the optic nerve is overstrained and the eye can be damaged.

 

5. poison

Pupil enlargement is a typical reaction to certain herbal and chemical poisons. Common blackthorn and belladonna can cause poisoning in which the pupils dilate. If chemical poisons such as chloroform or paraffin are ingested accidentally, they cause pupil dilation.