What Is The Standard Pupil Size And What Causes A Pupil Size Change?

For a general or average person, pupillary size measurement may seem something really unnecessary. But the fact is even a slight hormonal change, neurological change, circumstantial or even emotional alteration can make your pupil dilate. Now here, we are not going to talk about the details of pupil dilation. We will delve into the intricate details about the evaluation of pupil reaction and standard pupil size.

Standard pupil size, dilation and Constriction

Pupils, by biological nature, tend to get dilated or, better to say, get bigger in the low light zone. This change in pupil size lets lighter seep into our eyes, helping us adjust and see better in the dark. On the other hand, our pupils become smaller in bright light.

Now the real question is if we measure pupil size, what it will be in low or bright light!

Well, in the state of dilation, a pupil can measure between 4- 8 mm, but while constricted, it usually can be between 2-4 mm.

So it can be said that according to trusted pupillary evaluation, pupil size is usually 2-8 mm (American Academy of Ophthalmology)

What other things can cause pupil size change?

You might have noticed that a few people tend to keep a book or mobile close to their eyes in order to see well. That can be a sight that you need to see a doctor and get your pupils and eyes sight checked. Because looking something very close means you are straining your pupils to change its size to see better.

Looking at something very far or too close makes our pupil change its size. Though we cannot change its size consciously, it’s an auto-response. If we are looking at something very close to us, our pupils automatically become smaller. And to see something really far, it widens. Usually, we don’t feel anything when these minor yet impactful changes happen. But there are minor things that can be noticed, though. Like, a dilated pupil will always be sensitive to bright lights or even experience blurry vision too.

Before modern Ophthalmology, eye specialist doctors used to make the patient’s pupils dilated with medicinal eye drops to check their sights. But with time and new age pupillary evaluation, we can now vastly depend on pupilometers designed and manufactured by reputed companies like Neuroptics.

What exactly is Pupil?

Let’s make it simple. If you intently watch your eyes in the mirror under bright light, you will see the black center. Yes, that’s your pupil. It let the light ooze inside your eyes and reflect it on your retina to make you see things. Now the muscles that make or decide your eye color are located inside the iris, and they control the pupil.

Usually, we do have the same size of pupils in both of our eyes, but sometimes certain diseases, psychological upheavals, and particular medicines can make the pupil size fluctuate. Only a practiced ophthalmologist or neurologist can measure pupil size and let you know if there is anything you need to be worried about.

Health, Emotional state, and Pupil size

As we have already mentioned that there is a range of factors that can directly make your pupils change their size. Such as:

Light (we have already talked about it)

Emotional state:

A part of our brain that controls our emotions can make our pupil change its size. According to trusted pupillary size measurement surveys, sound or songs that can make you feel joy can also make your pupil wider.

If you are in front of someone with a bit dilated pupil, that can automatically make your pupils dilate too. That’s called pupil contagion and largely falls under emotional causes.

Particular drugs and medicines:

Sedatives (antihistamines and alcohol etc.), Anticholinergics, and Opiates (can constrict pupil).

Physical health and Ailments


If you are going through a concussion after smacking your head somewhere, your pupil can become bigger. In that case, evaluation of pupillary reaction can be necessary.

Cluster or One-sided Headache

Many of us have experienced a sort of excruciating headache that usually bothers one side of our face and can be felt behind our eyes. This sort of headache affects the nerves present in our face and can make our pupils become oddly small.

Wrap Up

Now, the thing is, as we already have stated, it is hard to notice any change in pupil size. And that is the very reason you should see an ophthalmologist or neurologist even if you have a slight ignorable doubt.

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