What the heck is a PD?

June 2, 2019

How to Measure Pupillary Distance – And Why It’s Important

-By Amy Lancaster

When looking for the perfect pair of glasses, what are some things you consider? Perhaps the shape of the lens, or the color and thickness of the frames. Have you ever tried on what you thought would be a pair that were made for you, only to realize that no matter how you morph them, you just cannot see properly out of them? Chances are, in this case, you came across the issue of incorrect pupillary distance.

“Excuse me?” You say as you stare at me with your skewed frames. “You mean like the length between my pupils?”

Yes, that’s exactly what we mean! Pupillary distance is the measurement of…well, distance – from one pupil to the other. This number is crucial when purchasing prescription glasses, as it guarantees that your center of focus is correctly aligned with the lens. Sure, you could buy any glasses from your local department store for convenience sake, but you will be saving yourself money and damage in the long-term if you know how to measure pupillary distance and order glasses accordingly (Plus – online glasses are cheaper anyway, wink wink).

It’s also important to know the difference between single pupillary distance and dual pupillary distance (yes, there’s more!). Single PD is the pupillary distance from the center of one pupil to the other – commonly used for any type of prescription glasses except for reading.

Dual PD, on the other hand, is the measurement from the center of one pupil to the bridge of the nose. This will normally be displayed as two numbers and written as a fraction – the left number being for the left eye, and the right number for the right eye (for example, 30/28).

So, how is this done? Normally, when you go in for an eye exam, your eye doctor will be taking into account your PD so they can record it on your prescription. While this number may fluctuate as you grow, normally by the time you’ve hit your teenage years, it shouldn’t change. Your optician can also take your PD measurement at your appointment with them if you don’t have the information on hand. If you want to measure for yourself, however, you can do this at home as well!

•Stand approximately 8 inches from a mirror.

•Take a ruler and hold it horizontally against your eyebrows, above your eyes.

•With your right eye closed, align the 0mm mark of the ruler in the center of your left pupil.

•Now, close your left eye and open your right eye, staring into the mirror to see what number is above your right pupil. That number is your single pupillary distance.

If you don’t have a ruler – never fear! We’re here to help you. Check out our guide on how to measure your pupillary distance. It even comes with a printable ruler, so you don’t have to go digging around for your own! We’ve even included a mirrored version so you can hold it up to a mirror without struggling to read the numbers.

The average single pupillary distance for adults is 54 – 74mm, while for children it’s 43 – 58mm. If you’re above or below these numbers, don’t worry! The point in measuring your PD is to make sure the optician makes your glasses tailored to you. We’ve got enough in the world to be self-conscious about; pupillary distance is not one of them.

“Hang on!” You yell with your newly fitted glasses (they look great, by the way). “What if I need reading glasses? How do I measure that?”

As we mentioned earlier, single PD can be used for most prescription glasses except for reading. Why? Because when you read, the focal point of vision from each eye changes and crosses. Calculating your reading glasses PD will be done by calculating the near PD (the prior measurements being the distance PDs). Simply subtract 3mm from your single/distance PD (for example, if your single distance PD is 58mm, your reading glasses PD will be 55mm). You can also calculate this with your dual PD number by subtracting 1.5 mm from each eye distance (example: if your dual PD is 30/28, your reading PD would be 28.5/26.5).

What’s your PD number? Do you have any horror stories of trying on glasses? Let us know in the comments!

 

 

 

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