How to Measure Your Pupillary Distance?

When you want to know how your pupillary distance can be measured you are in the right place. After reading this article you will know what tools can be used and what you should think about when performing the measurements. The pupillary distance can be measured with the following tools:

  • A ruler
  • A pupillometer
  • An app that analyzes a photo
  • An app that analyzes a video
  • Using a sample frame and a marker

With all the tools listed, you should have the same basic rules in mind to perform the best measurement possible. The person performing the measurement or your phone/camera should not be shifted more to one side or a parallax error will make one distance from one eye to the middle of the bridge smaller while it gets bigger for the other eye.

When the measurement is done the test person that is the one who wants to know the PD needs to focus on something that is 14 feet or even further away. This is crucial when measuring the PD. Because when the test person looks at something in front of him/her the eye will turn inward and will therefore manipulate the PD which is the measurement from the pupillary center when the test person looks into the distance straight ahead.

Oftentimes people measure the distance between both pupils in millimeters divide the distance by two and think they have the position defined correctly for where they look through. This is not the correct way to do it. The PD measurements should always be done with the already adjusted frame on your nose.

The reason is individual anatomical differences that could lead the actual frame to sit slightly shifted on your nose because of their shape. In some cases, people still want to know how big their PD is despite the drawbacks of this method. So let us begin with the ruler.

Using a Ruler to Measure Pupillary Distance

The cheapest tool to measure the PD which can be found in every household is the good old ruler. The ruler needs to be placed on the nose so the millimeters can be read on the ruler directly under the middle of the pupils. This is how easy it is to measure the PD with the ruler theoretically. In practice, a lot of people will not see if the PD is 62mm or 63mm. Or even something in the middle? Look at the picture and ask yourself. Can you read the millimeters accurately here?

An experienced optician measures the PD confidently. But in most cases, they do not use rulers anymore because of the issue I just described.

When the PD gets measured the person looking at the ruler needs to place his or her eye directly in front of the eye which gets looked at to check which millimeter marking perfectly aligns with the middle of your pupil. When the person observing the ruler and the pupils look from an askew angle the whole measurement will be false.

Can I Measure My PD With My Phone?

Yes, you can measure pupillary distance with a phone. There are a bunch of apps available. One of the easy-to-use ones is glasses on which gets a closer look at in the video below. Here are the download links below. All you need is a standard magnetic card so the app has something for reference when a picture is taken with your phone.

Glasses on for Android
Glasses on for iOS

The app will then guide you through the process. One thing to keep in mind which could cause trouble in some cases is the PD gets measured without glasses on. When the PD measurement is done without the frame on the nose you get the distances from the middle of one pupil to the middle of the other pupil. If your face would be perfectly symmetrical this would be right. However, assuming your nose is a little crooked then the whole measurement will deviate from the actual positions you will look through your glasses.

So this is still not the best option. Especially not with higher prescriptions. When this option is used you will be probably slightly off target and eye strain or headaches could be the case. I say this out of my experience as an optician.

An App That Uses a Photo or a Video to Measure Your PD

This is the professional version an optician or optometrist would use to measure your PD. The setup is more sophisticated to produce more reliable results. In reality, the experienced optician still will see the pitfalls as no tool is perfect. But what makes this approach a lot better as your DIY measurement is the perfectly pre-adjusted frame.

This way the optician knows where to place the optical centers of the lenses to ensure you get the best visual experience possible.

Using a Sample Frame and a Marker

While this approach is available to opticians for decades to measure the needed PD for the new glasses you could do the same. The same rules apply as mentioned above with the ruler to make sure the markings sit directly in front of the pupil. When you, not an optician this process looks pretty straightforward but will probably go wrong as you have no experience with how accurate you need to be with the markings. And with accuracy I mean there is no tolerance for a deviated marking.

Here in the picture above you can see the yellow points are directly positioned in front of the pupils. In comparison to that, the red markings are wider than the actual pupils. This could lead to problems you could more read about here in this article.

When you want to measure your PD with your phone or with the old ruler method you can do so. I personally as a master optician am not really enthusiastic about people performing that measurement themselves. The reason is just I saw so many bad examples where people do not know what the parallax error is. They are not positioning the ruler to parallel to their face as a frame would sit, gauge where they should not. And this is the experience I have with people learning the craftsmanship of an optician.

I wish you a great day.

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