Why are both of my pupils’ different sizes?

Most of us probably don’t spend much time looking at the shape or size of our pupils. Normally our pupils tend to be identical in terms of when and how much they dilate, but for some people, a differentiated pupil size can be indicative of an underlying health problem.

why are both of my pupils' different sizes

This is particularly common when other symptoms are present as well. Here are some of the main reasons for why your pupils are different sizes.


If you happen to notice that your pupils are dilating to different extents at the same time it might be that you have an eye condition called anisocoria. This condition means that your pupils will not necessarily be identical. For some people who have anisocoria, there is no impact upon one’s sight, which is termed physiologic anisocoria. However, if you also experience additional symptoms, such as drooping eyelids or fever, you ought to seek medical attention as soon as possible.

Horner syndrome

If you are experiencing a reduced pupil size on one side of your face it might be an indication that you are suffering from Horner syndrome. This syndrome is the outcome of a disruption of nerves between the brain towards the face and eye on one side of the body only. This syndrome typically results in a reduced pupil size in one eye and is joined by a series of other symptoms such as droopy eyelid and decreased sweating in the impacted side of your face and eye. If you are experiencing any of these symptoms then you should get medical attention immediately.

Being under the influence of drugs

Our pupils commonly increase in size when we are under the influence of recreational drugs which send stimulating signals to our nerves which can either increase or decrease the size of our pupils. This depends on the type of drug you have taken but in all cases our pupils resume to their regular size once the effects of the drug have worn off.

When to consult a doctor

While most of the time having unequal sized pupils results in little or no damage to one’s vision, for others the impact of differentiated pupils can be life-changing. For many people who do experience differentiated pupils, it is not a new condition and tends to be present from birth. However, if you have the symptoms of Horner syndrome described above, or if your pupils change size suddenly throughout your adult life, it is highly recommended to seek medical attention as soon as possible.

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