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Is it love? Nine reasons why your pupils may dilate

Ever wondered if you can tell what someone is thinking simply by looking into their eyes? Research has shown that our emotions play a part in pupil dilation and constriction, a completely involuntary action controlled by the autonomic nervous system.

You might have even heard that pupil dilation can signify that someone is attracted to you. But is this true? The experts at Lenstore have outlined all the reasons why our pupils might change in size and the potential meanings behind this uncontrollable reflex.

What are pupils and why do they change in size?

Our pupils are the dark circles in the middle of the eyes and are controlled by the muscles in the coloured section of the eye (the iris) which is managed by the branches of the autonomic nervous system. 

The pupils control how much light enters the eyes and can get bigger or smaller depending on how much light is around. When it is bright, they will reduce in size to limit the amount of light that enters your eye, and in low-light situations, the pupil will increase or ‘dilate’ to allow more light in.

Pupil size can decrease in size with age, but generally, a normal pupil can range in size from 2.0 to 4.0 millimetres (mm). Dilated pupils can be anywhere between 4.0 to 8.0 mm, which means they can double in size!


Do your pupils dilate when you look at someone you are attracted to?

The short answer is yes. Eye contact has been a central part of human interaction for a long time, so it’s no surprise that a change in emotion could cause the pupil to dilate. 

Research has found that heterosexual men are more attracted to women when their pupils are dilated. Being shown two photos of the same woman where the size of pupils have been altered to be different in each, men found women with larger pupils to be more attractive and open. The men described the woman with bigger pupils as “soft”, “pretty” and “feminine”, while characterising the woman with the reduced pupils as “hard”, “cold” and “selfish”. It should be noted that none of the men noticed the detail change in the photos.   

Other studies have also found that dilated pupils can be a response to arousal, and that size and darkness can be used to determine sexual interest

However, researchers have also found that women don’t respond to pupil dilation the same way as men. An experiment conducted by Selina Tombs and Irwin Silverman of the Department of Psychology at York University found that women prefer a range of different pupil sizes. They also found that heterosexual women who said they preferred short-term relationships were more attracted to pictures of men with larger pupils, while women who preferred long-term relationships were more attracted to smaller pupils.


Why does the pupil dilate when looking at someone you are attracted to?

The autonomic nervous system triggers various responses during emotions, such as arousal or happiness. The happy hormone, also known as dopamine, is produced when the body expects something good, such as a slice of cake or attention from a loved one. But the hormone can make the pupil widen as a side effect. It’s possible that when looking at a loved one and you notice that their pupils are dilated, it’s likely a sign they have strong feelings for you. 

What other emotions can cause your pupils to dilate?

Arousal and love are not the only emotions that can cause your pupils to increase in size. Other emotions such as anger, fear, and anxiety can result in pupil dilation. As a response to these emotional states, the pupil may dilate to better assess threats – just like some animal's pupils would when they’re getting ready to attack.


Other causes of pupil dilation 

Known by the medical term mydriasis, the pupil can dilate without any change in light or emotion. This can be caused by the use of certain medications, injury or disease. Here are some of the most common reasons that can cause mydriasis:


Some prescription and non-prescription medications can cause the pupil to dilate, as they affect the muscle in your iris that controls your pupils. Some of the medication that can cause this includes:

  • Medications containing botulinum toxin, such as Botox
  • Antihistamines
  • Medications for Parkinson's disease
  • Motion sickness medicines
  • Atropine 
  • Anti-seizure drugs

Eye injury

Damaging the nerves or the muscles in your iris that control your pupil can cause the pupil to dilate and become irregular in shape. This sort of injury can happen during a complication of eye surgery, such as a corneal transplant or cataract removal. 

Brain injury or diseases

After a head injury, stroke or tumour, pressure can build inside your brain, which can cause damage to the muscles in your iris that make the pupils open and close. Impacting one or both eyes, the pupils can remain dilated and not react to light. 

This is why during an eye exam, a doctor or nurse may shine a light into the patient’s eyes to see if the pupils get smaller. This is the same reason why athletes’ pupils are checked with a penlight after a head trauma during sporting competitions.

Recreational drug use

Illegal drugs such as cocaine, amphetamines, LSD, and ecstasy can cause the pupil to widen and slow down the ability of how the eye reacts to light. During the process of withdrawing from these drugs, pupils may stay dilated. 

Adie's pupil

Adie’s pupil, also known as tonic pupil, is a rare neurological disorder where one pupil is larger than normal and either does not contract in size or is slow to react in the presence of bright light. There is no cure for Adie’s pupil, and in most instances the cause is unknown. 

Congenital aniridia

Congenital aniridia happens at birth and usually occurs in both eyes. This rare condition is the partial or complete absence of the iris. As a result, there is no regulation of the amount of light entering the eye, which can cause sensitivity to light, resulting in large pupils. 

Congenital aniridia can be accompanied by other serious eye problems such as glaucoma, optic nerve disorders and nystagmus.

Benign episodic unilateral mydriasis

Benign episodic unilateral mydriasis is a harmless condition where only one pupil becomes dilated. Often accompanied by blurred vision, headache, and eye pain, it’s called benign as it’s not related to any serious conditions. 

The condition typically resolves itself without treatment, and the pupil returns to normal size within a few hours, but it can last for several days. 

When to see a doctor for dilated pupils

Emergency help should be sorted immediately if a head injury has occurred and the pupils look bigger, particularly if one pupil is larger than the other.

In most cases, dilated pupils are not a cause for concern, but sometimes they can highlight more significant issues. If the pupils are enlarged and don’t react to bright light, book an eye exam with a doctor or eye specialist. Once you have made sure your eyes are in tip-top condition, have a browse through our wide selection of lenses. We stock the best name brand daily, monthly & two-weekly contact lenses on the market.

Article originally posted in January 2019. It has since been updated.
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