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

However, if it remains dilated even without the light stimulus, then it is certainly no longer a physiological response and could indicate the presence of disease or pathological habits. Below we explain how the pupils work and what factors can cause their dilation, mydriasis .

How do the pupils work?

Pupils are the black circles in the center of our eyes that have the function of passing light to the retina to form 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 better vision, and sometimes it contracts to protect us from excessively luminous stimuli.

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

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

Types and causes of mydriasis

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

Factors that change pupil size causing mydriasis include some diseases and drug use. Below we present

Pharmacological causes

As the name implies, the pharmacological causes of mydriasis are those related to drug use. For example, the use of anticholinergics increases dilation , since they are substances that block the transmission of some chemicals to the eyes.

Another pharmacological cause is the recreational use of 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 causes dilation.

Medical causes

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

On the other hand, eye surgeries sometimes significantly damage the nerves that control the pupils or the iris. As a result, the pupils can take on different forms to react to light.

Physiological and neurophysiological causes

The physiological and neurophysiological causes of mydriasis are those 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 may lead to a temporary picture of mydriasis. This is because oxytocin is the substance that is released when we exercise and when we interact with people, both physically and socially. It is also the substance that is released during childbirth.

Also, mydriasis is often present during cranial nerve neuropathies, which are gradual damage to the nerves surrounding the eye. This affects the oculomotor system and the nerves that cause the pupils to widen or contract.

For example, parasympathetic nerve paralysis. Other related causes are strokes , head injuries, brain hernias or epilepsy.

Finally, one of the conditions that includes mydriasis is Benign Unilateral Episode of Mydriasis (BEUM), which is a temporary condition of pupil dilation, usually accompanied by headaches, eye pain, sensitivity to light and blurred vision. It usually occurs, for example, during some migraine episodes.

Treatment and what to do

In the case of mydriasis, it is important to keep an eye out for prolonged pupil dilation (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 .

As a treatment it is recommended to avoid direct exposure to the sun , as well as to avoid driving. It is also advisable to wear dark glasses and avoid reading texts at a short distance. Doing the opposite to 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 may recommend surgical treatment.