What Causes Pinpoint Pupils?

Pinpoint pupils may indicate an underlying condition that needs medical attention. Usually, pupils react to changing light levels by dilating in dark conditions and constricting in bright light. 

Many factors can affect pupil size, including medical conditions, prescription drugs, and substance abuse.

This article explains common causes of pinpoint pupils, accompanying symptoms to look out for, and when you should see an eye doctor.

What are Pinpoint Pupils?

Pinpoint pupils occur when the pupils shrink to become smaller than their standard size. 

A pupil is a circular opening at the center of the iris (the colored part of the eye). Pupils constrict in bright light to control how much light enters the eye. 

Generally, pupils are equal in size and function to achieve clear vision. The average adult pupil in bright light measures about 2 to 4 millimeters (mm) in diameter.¹ In dim lighting, it expands to 4 to 8 mm.

6 Common Causes of Pinpoint Pupils

Several things can cause pinpoint pupils. The most common causes include:

1. Prescription or Illicit Drug Use

Prescription opioids often relieve severe pain due to surgery, injury, or chronic illness such as cancer. However, some people use opioids as recreational drugs. 

Opioid drugs include oxycodone, morphine, hydrocodone, codeine, heroin, and others. When taken in excess, they contract the iris sphincter muscles, making the pupils smaller and unresponsive to light. 

Severe drug overdose will require emergency medical attention.

Other Symptoms

• Sleepiness
• Bloodshot or red eyes
• Hallucinations
• Cravings and sweating
• Nausea and vomiting
• Confusion or lack of alertness
• Slurred speech
• Drooping eyelids
• Difficulty breathing

Treatment

Opioids are highly addictive, and an overdose can be fatal if left untreated. During an opioid overdose, naloxone is often administered to block the action of opioids. 

Depending on the addiction level, several treatment options are available:

• Medical detoxification
• Behavioral counseling
• Support groups
• Recovery housing

2. Exposure to Toxins

According to the United Nations (UN) global review, about 200,000 people die annually from pesticide poisoning.² Some pesticides and herbicides can cause pupils to constrict. 

Nerve agents like sarin, soman, tabun, and VX are also known to cause pinpoint pupils.³

Although you may overlook exposure to toxins, pinpoint pupils are an excellent indicator for doctors.⁴

Other Symptoms

• Excessive saliva production
• Retching and vomiting
• Breathing difficulties
• Sweating
• Coughing
• Muscle weakness
• Rapid heartbeat
• Drowsiness
• Convulsions

Treatment

Any form of poisoning requires urgent medical care. If the person is unconscious or vomiting, make sure they're lying on their side with their head slightly tilted downwards. This will prevent choking on vomit. 

Treatment may include the following:

• Activated charcoal to prevent further absorption of the poison into the blood
• Antidotes, which reverse the effects of the poison
• Anti-seizure medications
• Sedatives to help the person relax in case of agitation
• Ventilators (breathing aids)

3. Anterior Uveitis (Eye Inflammation)

A pinpoint pupil may indicate anterior uveitis, also called iritis.  It's the most common form of uveitis, with an annual incidence of 20.3 per 100,000 people.⁶ 

Anterior uveitis may result from eye trauma or underlying medical conditions, such as:

• Rheumatoid arthritis
• Syphilis
• Tuberculosis (TB)
• Sarcoidosis
• Viral herpes

However, many cases of anterior uveitis have no identifiable cause (idiopathic).

Other Symptoms

• Red eyes
• Sore and inflamed eyes
• Blurry vision
• Light sensitivity (photophobia)

Treatment

Treatment for anterior uveitis may include prescription eye drops and anti-inflammatory drugs. Dilating eye drops may cause some blurriness or increase light sensitivity. However, your eyes will feel more comfortable.

Your doctor may prescribe oral steroids or injections if prescription eye drops fail. 

4. High Blood Pressure Medications

According to The Centers for Disease Control and Prevention (CDC), hypertension affects nearly half of the U.S. population, with men at a higher risk.⁷ 

Some prescription medications for hypertension, such as clonidine and tetrahydrozoline, can cause pinpoint pupils.

Other Symptoms

• Blurry or double vision
• Nausea and vomiting
• Tiredness
• Lightheadedness
• Headache
• Elevated heart rate
• Nosebleeds
• Shortness of breath

Treatment

If your high blood pressure medication is causing pinpoint pupils, talk to your doctor about alternatives.

5. Horner syndrome

Horner syndrome is a rare condition that affects the sympathetic nerve branch of the central nervous system, which mediates pupil dilation. 

According to research, Horner syndrome occurs in approximately 1 in 6,000 people and affects any age and ethnicity.⁹

Other Symptoms of Horner Syndrome

• A significant difference in pupil size (anisocoria)
• Drooping upper eyelid (ptosis)
• Slight elevation of the lower eyelid (upside-down ptosis)
• Little or delayed dilation of the affected pupil in low illumination
• Sunken eye
• Little or no sweating on the affected side of the face (anhidrosis)
• Lighter iris color in children (one year or younger)

Treatment

There's no specific treatment for Horner syndrome. In many cases, the condition will disappear after treating the underlying cause.

6. Head Injury

Head trauma can cause serious complications even if you don't notice it immediately. Studies investigating the relationship between traumatic head injury and pinpointed pupils indicate a possible effect on the pupil's reaction time.¹⁰ 

Seek medical attention immediately if you have a constricted pupil in one or both eyes following a head injury. 

Other Symptoms

• Loss of consciousness or coma
• Persistent or worsening headache 
• Vomiting or nausea
• Blurred vision
• Convulsions or seizures
• Clear fluids draining from the nose or ears
• Weak or numb fingers and toes
• Loss of coordination
• Cognitive or mental symptoms
• Confusion and memory problems
• Slurred speech
• Change in eating or nursing habits (children)

Treatment

Over-the-counter painkillers can help with pain relief. Antinausea drugs will also help in case of nausea or vomiting.

Your doctor prescribes anti-seizure medications such as carbamazepine, clobazam, levetiracetam, clonazepam, etc. These medications work by stabilizing the brain's electrical activity.¹¹

Less Common Causes of Pinpoint Pupils

Other factors that can cause pinpoint pupils include:

• Certain medications, such as Lomotil for diarrhea and phenothiazines for schizophrenia
• Antipsychotic medications
• Medications to treat glaucoma
• Neurosyphilis (syphilis of the brain)
• Deep sleep
• Iridocyclitis (inflammation of the iris and ciliary body)
• Aphakia (absence of the natural eye lens)

When to See a Doctor for Pinpoint Pupils

Seek medical treatment if you notice your pupils shrink for no reason. Your eye doctor will give you a proper diagnosis and recommend the best medicine. 

In case of an overdose, contact 911 for immediate assistance. 

Getting prompt medical care can help prevent life-threatening complications, such as stroke due to head trauma or death from a drug overdose.

Diagnosis

To diagnose pinpoint pupils, your doctor will conduct a comprehensive eye exam. Your doctor will observe your pupil size, appearance, and behavior in bright and normal lighting conditions.

They may also administer dilating eye drops to rule out any eye diseases. If you're diagnosed with tiny pupils, your doctor will investigate the cause and commence treatment.

Additional diagnostic testing may include:

• Magnetic resonance imaging (MRI)
• X-rays
• Computerized tomography (CT)
• Toxicology screening
• Blood tests
• Urine tests 

Because pinpoint pupils are a symptom, not a condition, your doctor will ask about any accompanying symptoms you have.

Treatment

There’s no specific treatment for pinpoint pupils. This is because it’s not a disease but a symptom of several conditions. 

Your doctor must identify the underlying issue to determine treatment for pinpoint pupils.

Outlook

The outlook for conditions that cause constricted pupils is better when people seek treatment as soon as possible. It’s also essential to follow the advice of any medical professionals you work with.

If you use illicit drugs, tell your doctor about it when you go for treatment.

With anterior uveitis, permanent eye damage may occur if left untreated. 

Poisons from insecticides or nerve agents can be deadly if not treated properly. Seek immediate medical attention for suspected poisoning.

Summary

Pinpoint pupils are abnormally small pupils. This condition is known as miosis or myosis.

Several factors can cause a pinpoint pupil, including eye disease, substance abuse, prescription drugs, other drugs, exposure to toxins, and head injuries.

If you have pinpoint pupils, your doctor will conduct an extensive eye exam to determine the cause and recommend treatment.