Most people are usually familiar with what dilated pupils are, and chances are you are as well! When you were younger you might have shone a flashlight into one of your eyes and watched your pupil shrink before moving the light away and watching it dilate again.
You might also recall your most recent visit to the eye doctor where your doctor put some special eye drops in your eyes to dilate your pupils. By opening up your pupils, eye doctors can take a better look at your eyes and examine them more closely for any abnormalities.
In regular lighting your eyes also adjust. When you walk into a dark room after being in a light-filled room, it can be difficult to see. However, when you give your eyes time to adjust, the pupils dilate (expand) to take in more light and you can see.
Similarly, when you walk out of a dark theater into a sunny parking lot, you might feel blinded by too much light. That’s because when you’re sitting in a dark theater, your pupils dilate, but the sudden move from a dark theater to a sunny area is faster than your eyes adjust. After a few moments in the parking lot, your eyes soon adjust and you don’t feel as blinded anymore.
These situations are ones that a lot of us are familiar with, but what about other instances that cause dilated pupils?
Did you know that certain drugs can cause dilated pupils? In today’s blog, we’ll explore why pupils dilate, what substances cause dilated pupils, potential risk factors of dilated pupils, and managing dilated pupils.
What Are Pupils and Why Do They Dilate?
Pupils are the black circle in the center of your eye. Pupils shrink (constrict) and grow (dilate) in response to varying light levels. Their function is to let light in and direct that light to your retina, which are the nerves at the back of your eye, allowing you to see.
Pupils constrict and dilate through muscles in your eye that are located in the iris. The iris is the colored ring of your eye. The iris is what people will look at to determine what color eyes you have. For example, people with a blue iris have blue eyes and people with a brown iris have brown eyes. Each iris contains the muscles necessary to manipulate the pupils.
Under normal conditions, pupils are usually the same size. According to healthline, a normal pupil measures approximately 4 to 8 millimeters when fully dilated and 2 to 4 millimeters when constricted.
A Variety of Reasons for Pupil Changes
There are a variety of reasons why pupils dilate or appear to be different sizes that go beyond changes in light levels. These range from everyday occurrences to mental conditions and even substance use.
- Distance of objects you’re looking at
- Pupils also naturally dilate or constrict based on distance in addition to light levels. Focusing your gaze on something closer to you will cause your pupils to constrict. Casting your gaze towards something farther away will cause your pupils to grow.
- Concussions
- You’ve probably heard of concussions before. Maybe you’ve even experienced one before. They’re especially discussed a lot in the realm of contact sports. A concussion is a brain injury that usually results when a hard impact or blow to the head causes the brain to smack into the skull. This can result in a person’s pupils becoming asymmetrical, with one pupil noticeably larger or smaller than the other.
- Anisocoria
- Anisocoria is the name used to describe the condition in which pupils happen to be different sizes that aren’t a result of injury to the head. According to the American Academy of Ophthalmology, 1 in 5 people naturally have anisocoria. Many of these people have absolutely no problems that stem from their pupils being two different sizes.
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- However, we should caution that sometimes, anisocoria can sometimes be a sign that there is a more serious eye problem. See an eye doctor if you are concerned about this condition. The American Academy of Ophthalmology explains that people with anisocoria could have
- A nervous system problem
- A history of eye damage
- A risk of having a stroke
- An infection
- Adie’s tonic pupil (a condition in which one pupil doesn’t respond to light as well as the other)
- However, we should caution that sometimes, anisocoria can sometimes be a sign that there is a more serious eye problem. See an eye doctor if you are concerned about this condition. The American Academy of Ophthalmology explains that people with anisocoria could have
- Cluster headache
- A cluster headache refers to a specific kind of very intense headache that affects one very focal point of the face. Typically, cluster headaches take place behind the eye and can be very painful. The name “cluster headache” refers to the multiple headaches that occur within an episode. Some people may experience up to eight headaches in one day. The pupil can shrink throughout the duration of these headaches.
- Iritis
- Iritis is a condition in which the iris, the colored ring of your eye, experiences some inflammation. Inflammation can occur for a variety of reasons including infection, trauma, and autoimmune diseases. Because the iris contains the muscles necessary to control the pupil, problems with the iris in cases like iritis can cause abnormally sized pupils.
- Horner’s syndrome
- Horner’s syndrome is a condition in which an individual has a disrupted nerve pathway or a nerve pathway that has been damaged. This nerve pathway runs from the brain to the face and eye. Injury to that nerve pathway can cause pupils to constrict.
- Your emotions
- It might sound a bit strange, but your emotions can affect how your pupils look! The International Journal of Human-Computer Studies published a 2003 study that found the dilation of pupils as a reaction to emotional stimuli such as laughter or a baby crying.
- Illicit substance use
- Illicit substance use is one of the prominent side effects from a variety of different drugs. Substance use can both constrict and dilate pupils depending on the substance. We’ll take a look at which drugs do what in our next section.
- Prescription medication
- Although illicit substances get most of the attention when it comes to pupil dilation and constriction, prescription medication or medication that you can get over the counter can also affect the iris’ muscles. The next section will cover which prescription medications can affect pupil dilation or constriction in more detail.
Illicit Substances and Prescription Drugs That Affect Your Pupils
A variety of drugs have the power to affect pupil size because drug interactions in the body often affect neurotransmitters in your brain. Neurotransmitters are chemical messengers in your body. The interactions and messages between neurotransmitters are key in operating your body’s central nervous system. The interactions between neurotransmitters help control your bodily functions and enact proper functions.
Many drugs, due to their chemical makeup and the chemical reactions they cause in your body, can cause neurotransmitters to be affected. Because neurotransmitters play a role in your pupil size, a variety of medications and illicit substances affects the appearance of your pupils.
Prescription and over-the-counter drugs that can affect pupil size include
- Anticholinergics
- Blocks acetylcholine, a compound in the central nervous system that functions as a neurotransmitter
- Anticonvulsants
- These medications are often prescribed to treat epilepsy and seizures. In order to limit the severity or frequency of epilepsy and seizures, anticonvulsants alter neurotransmitter activity and nerve impulses.
- Antidepressants
- Many antidepressant medications target serotonin and norepinephrine. These two are chemical messengers that control many bodily functions.
- Antihistamines
- Antihistamines are often used to help relieve the symptoms of a variety of allergies. They work by blocking the immune system’s response to allergy symptoms like sneezing or an itchy or closing throat. For example, Benadryl® is a well-known antihistamine.
- Benzodiazepines
- Although they are often associated with substance misuse, benzos can also be legally prescribed. There are, however, some unfortunate cases in which individuals become hooked on benzos and begin to misuse them. Benzos impact a particular neurotransmitter that relaxes muscles.
- Decongestants
- Decongestants typically shrink blood vessels in order to address swelling and inflammation.
- Dopamine precursors
- Dopamine precursors boost levels of the neurotransmitter dopamine in the body. Since dopamine is responsible for many bodily functions, pupils can also be affected.
- Mydriatics
- Mydriatics are also known as the eye drops that dilate your eyes. When you go to the eye doctor or need to undergo a particular eye surgery, these eye drops are used to take a better look in your eyes.
- Stimulants
- Prescription stimulants are used in the treatment of attention-deficit/hyperactivity disorder (ADHD). Stimulants are well known for causing pupils to dilate.
- Selective serotonin reuptake inhibitors (SSRIs)
- SSRIs are often used in treatment for depression since they boost serotonin. Low levels of serotonin can cause depression, anxiety, and sleep trouble.
Commonly misused drugs that dilate pupils include:
- Amphetamines
- Bath salts
- Benzodiazepines
- Cocaine (including crack cocaine)
- Crystal methamphetamine
- Ecstasy
- Ketamine
- LSD
- MDMA
- Mescaline
Commonly misused drugs that constrict pupils include:
- Oxycodone
- Fentanyl
- Heroin
Are There Permanent Side Effects To Dilated or Constricted Pupils?
When you experience dilated or constricted pupils as a result of substance use, you might wonder if your pupils could permanently remain in such a state. The good news is that pupils usually return to a normal functioning state after the side effects of drug use have worn off.
You should note, however, that some drugs can cause pupil dilation during the withdrawal period. Opioids in particular can cause pupil dilation during withdrawal.
There are not many long-term studies of the effects of whether consistent drug use can cause permanent changes in pupils. More ongoing research will be able to give a clearer answer in the future.
Managing Your Pupil Dilation: Asking For Help
When your pupils are dilated as a result of drug use or any other reason, they can cause you discomfort. Remember: dilated pupils let in greater amounts of light. When you take in more light, normal light levels like an average sunny or semi-cloudy day can seem overwhelmingly bright to you.
You will probably be very sensitive to any light sources while your pupils are dilated. To help make yourself more comfortable, you can wear protective eye gear to help shield your eyes from light levels.
For example, many people use either photochromic lenses in their glasses or wear sunglasses. Photochromic lenses adjust to the light levels automatically, darkening and lightening in response to sunny or dark environments. Sunglasses, of course, help block glare from the sunlight and can keep your sensitive eyes well protected from the sun’s rays.
If you ever have any major concerns about abnormal pupil sizes, consult with an eye specialist to ensure you remain involved and aware about your health.
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Frequently Asked Questions
Which drugs make your pupils smaller?
Opioids generally make your pupils smaller. Smaller pupils are also known as “pinpoint pupils.” Commonly misused opioids include oxycodone, fentanyl, and heroin.
Can medication cause dilated pupils?
Yes, both prescription, over-the-counter, and illicit drugs can all cause dilated pupils. Drug interactions in the body often affect neurotransmitters in your brain. Neurotransmitters are chemical messengers in your body. The interactions and messages between neurotransmitters are key in operating your body’s central nervous system.
What drugs dilate and constrict pupils?
Drugs that can dilate pupils include: antihistamines, anticonvulsants, anticholinergics, antidepressants, benzodiazepines, decongestants, dopamine precursors, mydriatics, stimulants, selective serotonin reuptake inhibitors, amphetamines, bath salts, cocaine, crystal meth, ecstasy, and ketamine.
Drugs that constrict pupils include: oxycodone, fentanyl, morphine, codeine, and heroin.
