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Pupils that Differ in Size

If you notice that you or a loved one has different sized pupils, it’s important to understand the potential causes and to know when to be checked by an eyecare professional.

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Table of Contents

Overview

The pupils in our eyes are the black circular part at the front of the eye which allows light into the back of the eye. The size of the pupil changes depending if you are in a brightly lit environment versus a dark one. In a dark setting, the pupils widen in order to take in as much light as possible. In contrast, in bright light, the pupils constrict. 

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What Causes Different Pupil Sizes?

Anisocoria is a medical term used when the pupils are different sizes. One in five people don’t have pupils that are exactly the same size, but the difference is small and insignificant, often a 1mm difference between both eyes. This is considered to be physiological anisocoria which causes no harm. However, there are conditions which cause the pupils to differ in size and it can be a sign of a serious medical disease.

Some medical causes of anisocoria include:

  • Virus 
  • Issue with the nervous system, for example: Adie’s tonic pupil
  • Eye injury
  • Brain tumor 
  • Aneurysm 
  • Seizure 
  • Complications of eye surgery
  • Oculomotor nerve palsy
  • Horner’s syndrome 
When to Seek Immediate Care

When to Seek Immediate Care

If you notice a sudden change in the size of one of your pupils, especially if it occurs after an injury or along with other symptoms, it’s important to seek medical care right away. It is not necessarily a harmful phenomenon but it does need to be checked as soon as possible because some of the possible causes are serious and require immediate medical care. Please schedule an appointment at our office and we will do our best to accommodate an appointment right away. If that is not possible we will guide you to the best urgent care facility.

Symptoms

Symptoms

It can be hard to notice a change in the size of your pupils, especially if your pupils blend in with a dark colored iris, as opposed to someone who has light blue eyes. Sometimes anisocoria occurs with other symptoms which are more noticeable, such as:

  • Difficulty moving your eye
  • Pain in the eye
  • Droopy eyelid 
  • Fever 
  • Headache
  • Less sweating than usual
  • Stiff neck

If you notice any of these symptoms along with different sized pupils or experience sudden changes in your vision, please schedule an eye exam with your eye doctor.

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Treatment

Treatment

Most of the time anisocoria does not require treatment as it does not affect the health of your eyes or your vision. If it does happen to affect your vision, your eye doctor may be able to prescribe appropriate glasses that can help with the issue. If the difference in pupil size is due to a medical condition, this underlying cause will be treated appropriately. If you have any questions or concerns regarding anisocoria, make sure to consult with your eye doctor who can guide you, diagnose the condition and recommend the proper treatment.

Prevention

Many cases of anisocoria cannot be prevented as it could be physiological or due to medical conditions that can’t be avoided. However, anisocoria could be related to eye injuries and it’s important to do what we can to avoid such circumstances. If you are engaged in any activities that pose a threat to your eyes, it is crucial to ensure that you are wearing the proper protective gear in order to prevent trauma to the eyes.

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Common Questions

Adie’s tonic pupil is a disease that affects the nervous system. The nervous system is made up of the brain, spinal cord and nerves. It also controls the pupils and their response to different light conditions. If the room is dark, the pupils are supposed to widen to allow us to see better. In an environment that is lit up, the pupils are supposed to constrict. Adie’s pupil usually only affects one pupil and it prevents the pupil from constricting properly when exposed to light. This condition is not life-threatening and with proper treatment, a person with this condition can live a normal healthy life.
The eye doctor will measure the diameter of your pupils under light conditions and in darkness. In addition, the pupil can be further examined using the slit lamp which is a special microscope that allows the healthcare professional to observe your eyes in greater detail.
Different-sized pupils in children are not necessarily caused by underlying disorders. A difference in pupil height might be genetic if other members of the family also have similar pupils. Additionally, for unknown reasons, pupil sizes may temporarily differ. Anisocoria, however, can be caused by serious, life-threatening conditions such as stroke, brain aneurysm or cancer. In the event that you notice a change in your vision or eyes, you should see our eye care provider right away.
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Summary

Physiological anisocoria is a common phenomenon, found in approximately 20% of the population. It is not harmful and it’s a very minor difference in the size of both pupils. There are other types of anisocoria which present with a more significant inequality of sizes between the pupils. This could be harmless or it could be caused by an underlying medical condition. If you suddenly notice that one pupil is bigger or smaller than the other, especially after trauma to the eye or if it comes with other symptoms, you can reach out to your nearest Amplify EyeCare practice either via a call or in-person visit. Regardless of the type of anisocoria, it is important to get it checked by the eye doctor for a proper diagnosis and discussion of treatment, if relevant.

 

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