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Mydriasis (extreme dilation of the pupil): symptoms, causes and treatment

Mydriasis (extreme dilation of the pupil): symptoms, causes and treatment

January 6, 2023

We know as mydriasis the phenomenon of widening of the pupils (to the dilation of pupils), which can be caused by factors both internal and external to the organism itself. It is the process opposite to miosis (the reduction of the size of the pupil) and it is usually a physiological response to light and brightness.

However, if it remains dilated even without the luminous stimulus, then surely it is no longer a physiological response and could be an indicator of the presence of diseases or pathological habits. Next we explain how the pupils work and what factors can cause your dilation, mydriasis .

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How do the pupils work?

The pupils are the black circles that are the center of our eyes and that have the function of passing light to the retina to form the images. They are surrounded by the iris and the cornea , and are composed of an opening that widens or contracts to give way to light. Sometimes it widens to allow us a better vision, and sometimes it contracts to protect us from excessively bright stimuli.


However, the pupils are activated as an automatic response to various factors (not only light), and the system that is responsible for controlling their activity is the autonomic nervous system, which in turn is divided into the sympathetic nervous system and the nervous system. parasympathetic.

When the reason for the widening of the pupil It is not only related to our physiology and our vision , then the mydriasis can be an indicator of the existence of a pathological condition, or, it can indicate that recently a substance that alters the nervous system has been consumed.

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Types and causes of mydriasis

Mydriasis is a natural and quite common phenomenon, which helps us to properly perceive light when it is presented in large quantities. However, in some cases, mydriasis It is not caused by exposure to light but by other elements that also affect our body .


Among the factors that change the size of the pupil causing mydriasis are some diseases and the use of drugs. Next we will present

Pharmacological causes

As its name says, the pharmacological causes of mydriasis are those that are related to the use of drugs. For example, the use of anticholinergics increases dilation , since these are substances that block the transmission of some chemicals to the eyes.

Another pharmacological cause is the use of recreational psychotropic substances, such as cocaine, ecstasy, hallucinogens, methamphetamines or THC. This is because these substances affect the serotonin receptors in the brain (depending on the type of drug they increase or decrease their secretion), which generates dilation.

Medical causes

The medical causes are those that are related to a surgical intervention that has between its effects the dilation of the pupils. For example, surgeries to treat brain injuries cause mydriasis because they increase the pressure on the skull, which affects the eyes.


On the other hand, surgeries in the eyes sometimes severely damage the nerves that control the pupils or the iris. As a result, the pupils can adopt different ways of reacting to light.

Physiological and neurophysiological causes

The physiological and neurophysiological causes of mydriasis are those that are related to our biological or neuroanatomical functions. Specifically, they are the causes related to how our brain and other related systems work.

The presence of high levels of oxytocin It can lead to a temporary mydriasis. This is because oxytocin is the substance that is released when we exercise and when we relate to people, both physically and socially. It is also the substance that is released during childbirth.

Likewise, mydriasis is usually present during neuropathies of the cranial nerves, which are gradual damage to the nerves that surround the eye. This affects the oculomotor system and the nerves responsible for the pupils to widen or contract.

For example, paralysis of the parasympathetic nerve. Other causes related to this are strokes , cranioencephalic traumatisms, brain hernias or epilepsy.

Finally, one of the symptoms that include mydriasis is the Benign Unilateral Episode of Mydriasis (BEUM), which is a temporary condition of dilatation of the pupil, usually accompanied by headaches and eyes, sensitivity to light and blurry vision. It usually happens for example during some episodes of migraine.

Treatment and what to do

In the presence of mydriasis, it is important to watch for dilatation of the pupil for a long time (if the light stimulus has disappeared or enough time has passed to adapt to it). In these cases it is important to consult a specialist doctor .

As a treatment it is recommended Avoid the direct exposure to the sun , as well as avoid driving. It is also advisable to use dark lenses (glasses) and avoid reading texts at a short distance. Doing the opposite of all these recommendations can cause mydriasis to remain and significantly affect our vision.

On the other hand, if it is an indicator of pathological condition, the specialist could recommend a surgical treatment.


What Drugs Cause Your Pupils To Dilate? (January 2023).


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