Why do some adults have small pupils in one or both eyes?

Why do I have a small pupil?

Variations in the size of your pupils – the dark point in the centre of your eye – can be completely natural and are usually harmless.

However, if you’ve noticed a change that seems unusual or you’ve recently had a head injury, you need to know what the reason is so you can take steps to rectify the problem.

What does it mean when your pupils seem smaller than usual?

We run through 5 of the most common causes of tiny pupils and how to treat them.

1. Narcotics

The use of narcotics is one of the most common reasons for pinpoint pupils.

Whether you’re using a narcotic-based painkiller like fentanyl or codeine or an opioid drug like heroin or methadone, your pupils shrink because of the way the drug interacts with the nervous system.

Discontinuing use will return the pupils back to their normal size.

2. Horner’s syndrome

Horner’s syndrome affects the bodies fight or flight mechanism and may be caused by underlying symptoms like stroke or a tumour.

If your pupils seem abnormally small and you also have a drooping eyelid, then the nerve that keeps your pupil dilated isn’t working properly.

In most cases, no treatment is required.

3. Iritis

When the coloured part of the eye becomes inflamed, it can cause the pupils to shrink.

There may also be other symptoms including a headache and bloodshot eyes, and you’re likely to experience pain if a bright light is shone into the eye.

The good news is that this painful condition can be treated with eye drops, although you may need a steroid injection near the eye if the infection is very bad.

4. Bleeding in the brain

A bleed in the brain can be caused by unchecked high blood pressure. A bleed near the brain stem can cause both pupils to constrict.

You will need an MRI scan to pinpoint the bleed and then surgery to stop it.

5. Exposure to chemical nerve agents

Although these types of toxins are used in chemical warfare, regular garden insecticides can have the same effect.

If you think you’ve been exposed to organophosphate poisoning, get tested and decontaminated as quickly as possible. You’ll probably be treated with pralidoxime and given oxygen.

Looking for more answers?

We’ve answered more of your common questions relating to pupil size:

When you should see a doctor

Underlying conditions like mumps and rheumatoid arthritis can cause infections that can lead to pinpoint pupils.

Less common causes of small pupils include the use of magic mushrooms or neurosyphilis, a bacterial infection as a result of syphilis that has been left untreated.

Because pinpoint pupils are a symptom, not a disease, you’ll need to consult your doctor if you notice any changes to your pupils. They can then deliver appropriate treatment.

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