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The pupil is a part of the iris and can change its size according to the light in the environment around. In darker conditions that pupils dilate and become wider to allow as much light as possible to enter, while in brighter conditions the pupil becomes smaller to restrict the amount of light that goes in.

There is some natural variation in the size of the pupils. Like other parts of the body, some people can have a larger pupil while other may have a smaller one. It is noted that children often have larger sized pupil and are in fact quite common.

If these pupils are equal sized and react normally to change in light exposure, then there is nothing to worry about. If however, the pupils are fixed and do not react to change in light then there is something to be concerned about. A fixed pupil is called as Mydriasis.

There can be many causes for a fixed pupil to occur.


The pupils can be dilated during times of intense emotion like anger, happiness, sexual excitement or even fear. These causes, however, are not permanent and the normal function of pupils should reappear soon after.

Nervous disturbances

The muscles controlling the dilation of the pupil are under involuntary neural control. This means that a person cannot decide to not allow the pupils to dilate or make them dilate more than normal. Certain conditions like a brain stroke, seizure, epileptic attack, nervous disorders or an increased amount of pressure in the cranium can result in the occurrence of mydriasis.


A direct trauma to the head or even the face can cause damage to the nerves that supply the eyes. The damage usually occurs to the optic nerve or even the muscles controlling the iris. The result is a nonresponsive pupil or unevenly sized pupils in the two eyes.


Prescription medication used in the treatment of a cold or a stuffed nose can cause a fixed pupil as a side effect. Make sure that any and all medication being taken by the child is informed to the doctor. Antihistamines, anticholinergics, antidepressants, medicinal eye drops usually given before an eye exam and other illicit drugs can cause the pupils to dilate.


Some harmful chemicals and even dangerous plants can have the effect of dilating the pupil. Children can be exposed to these substances unknowingly and will most likely be tested for them when the doctor is ruling pout possible causes.

Certain kinds of chemicals, exposure to benzene, chloroform or even jet fuel can cause mydriasis.  

Symptoms associated Mydriasis

 A few of the things that a patient or those around the affected person will include bouts of nausea, slurring of the speech, numbness, difficulty in focusing on things, delayed response to stimulus or even complete unresponsiveness.

The patient may also have a difficulty in controlling their bladder/bowel movements, complain of a severe headache, and undergo hallucinations.

Some of the most critical signs, usually seen in life-threatening cases, include coma, loss of muscular tone and the body going in a state of shock.



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