What are Dilated Pupils?

Steve R.

A person with dilated pupils is easy to recognize because his or her pupils will appear larger than usual. Pupils are the dark circles located in the middle of the eye. A pupil is surrounded by the iris, the colorful membrane of the eye. Fastened to the iris are muscles that control the size of the pupil. When these muscles pull on the iris, pupils dilate.

Psychedelic drugs like marijuana cause the pupils to dilate.
Psychedelic drugs like marijuana cause the pupils to dilate.

The main purpose of the pupils is to let light pass through the eye. Pupils dilate and contract, according to the amount of light needed. When light is limited, or there is complete darkness, eyes naturally dilate in attempt to allow more light to flow in. If the pupils remain dilated even in bright light, however, this could be an indication of a condition that may require medical attention.

Dilated pupils allow the doctor to get a better look at the retina and iris.
Dilated pupils allow the doctor to get a better look at the retina and iris.

Medically, when the pupils are dilated when they would not normally be, the condition is referred to as mydriasis. In itself, dilated pupils are not a serious condition. If the eyes are exposed to light for too long during dilation, however, it can damage a person's vision.

Some antidepressants and other medications contribute to pupil dilation.
Some antidepressants and other medications contribute to pupil dilation.

In addition, it is possible that the dilation is a symptom of a more serious medical issue, including life-threatening conditions such as hemorrhages, brain tumors, aneurysms, or hematomas. The ingestion of toxic chemicals or many types of medicines and drugs can also cause the pupils to dilate. Diagnosing the cause of severely dilated pupils requires an eye exam, as well as a physical and neurological exam.

Normally, a person's pupils contract when light is bright.
Normally, a person's pupils contract when light is bright.

Head trauma or trauma to the eye may induce dilated pupils. After an injury, the iris can be affected, causing the pupil to not constrict normally. A condition called Adie's tonic pupil syndrome can also affect pupils to dilate. This condition, mostly affecting young adult females, causes the pupils to react slower than usual to light.

Medication, including antihistamines and antidepressants, can affect pupil dilation. Some drugs, such as psychedelic, including LSD and marijuana, and psychostimulants, such as amphetamines and methamphetamine, may cause dilated pupils. In addition, withdrawing from narcotics can also cause pupil dilation.

Sometimes eyes are dilated on purpose, usually when an individual goes for an eye exam. During the visit, the doctor will often place medicinal drops called mydriatics into the eyes. The medicine forces the eyes to dilate, allowing the doctor to get a better look at the retina and iris, and to also see how the eyes react to light.

A person with dilated pupils.
A person with dilated pupils.

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Discussion Comments


I think my pupils dilate more than most peoples' do although there's no way to be sure. I have found that if I'm looking up at the same patch of stars as someone, the seven sisters for example, I can see more of them than most people, even though I wear glasses which would theoretically blur my vision a tiny bit.

I also squint more during the day, so it's not always the best thing in the world.

I know there are special colored lenses that simulate extremely dilated eye pupils. I like to think I look like I'm wearing those in the dark!


@drtroubles - It is not a sure and certain sign that he is using drugs, but it is a pretty good one. The thing is, other things that cause pupils to dilate can also cause mood swings. Like brain tumors for example, or like genuinely prescribed drugs.

If your friend was recently put on certain antidepressants for example, they can cause mood swings and dilated pupils in some people.

However, if your friend has used illegal drugs before, that is the most likely explanation.

Have you had a frank, non-accusatory talk with your friend?

Even if you know for sure that they are doing drugs, there's not much you can do besides this, unless you turn them in to the police.


Does anyone know if dilated pupils are a solid way to identify substance abuse? I have a close friend who has been actually strangely recently. He goes from being very agitated to mellow, and worry that he may be using drugs again.

I have often noticed that his pupils seem absolutely huge, and would like to confront him about it but I really want to make sure I am not jumping to conclusions first. I honestly believe that he is partaking in some seriously self-destructive behavior and I would like to get him some help if he is falling into old patterns. It is just tough when someone is being secretive.


@strawCake - Having your pupils dilated is definitely one of the worst experiences I have had too. For myself I have oodles of eye issues and my optometrist always wants to take a good look into my eyes, which leads to fairly regular appointments with her for pupil dilation.

An optometrist can see really well into the back of your eyes once the pupils are dilated but I must say the whole process can really give you a headache.

For anyone who has been told they are going for pupil dilation, bring very dark sunglasses to wear afterwards. Also, if you're allowed take a few painkillers for the headache to make things easier.


@strawCake - That doesn't sound like a very fun time at all! It sounds like you made the best of it though.

I take antihistamines and I feel pretty sure they make my pupils dilate a little more than normal. I've never really given it much thought until I read this article but I feel like my eyes are way more sensitive to sunlight since I started taking them. I really need the antihistamines so my solution to this problem is to keep sunglasses on me where ever I go.


I had my pupils dilated at the eye doctor a few years ago and I really did not enjoy the experience at all. I know they had to do it for a good reason but I hope I never need it done again!

After they dilate your pupils it literally takes hours for them to go back to normal. During this time your eyes are super sensitive to light. My old eye doctor was in a mall and I didn't have any sunglasses with me so I ended up having to wear this ridiculous cardboard pair they gave me.

The only thing I could think to do while I was waiting for my pupils to resume their regular size was see a movie. Sitting in a dark theater was a lot better on my eyes than stumbling around in the light wearing a pair of silly glasses!

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