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The Pupil Distance (PD) measurement needed to buy prescription glasses
How to get your Pupil Distance measured
What is the PD?
The PD is what it sounds like it is the distance between your pupils which we measure in millimeters (the normal range is between 54-74mm)
How do I get my PD?
Ask your eye doctor or local optician to measure it for you. It will only take a couple of minutes. or read below how to do it on your own.
Asking a friend to help you measure your PD:
This is the easiest method for measuring your PD. With your friend sitting opposite you at the same height ask them to place a ruler across the bridge of your nose with the millimeter side facing upwards.
Next ask your friend to close their right eye and you then look directly into their left eye. Ask your friend to slide the ruler so that the zero value is in the center of your right pupil and to keep the ruler very steady across your bridge. Then ask your friend to close their left eye and for you to look directly into their right eye.
Your friend will then read off the measurement to the center of your left pupil. And that's it!
Using your current glasses to measure your PD with help from a friend:
Put your glasses on so that they are comfortable and steady. Ask your friend to stand opposite you and mark on your lenses the position of your pupils with a non permanent marker.
You should now see two lines directly in front of you whilst wearing your spectacles. Take off your glasses and measure the distance between the two markings. And that's it!
The Pupil Meter
You can try the tool below - it has step by step instructions using your computer and a credit card:
The Pupilmeter will measure your pupil distance (PD) for far/distance using your webcam. It takes any standard sized plastic card with a magnetic strip (such as a credit or debit card), your smiling face, and a couple of minutes of your time. When used properly, the Pupilmeter has been found to be accurate within 0.5mm. This is not a substitute for having your PD measured by an eye care professional when possible.
Absolutely no data or images are stored when you use the Pupilmeter. Please make sure to read and follow the instructions carefully.
Use instructions above on how to use the online Pupil Meter
When done: Please enter your P.D. measurement into the prescription form when making an order.
Known Scale of Measure - Magnetic Strip Card
The PupilMeter uses an image of your credit card for scale of measurement, much like a distance scale on a map. No information about your credit card is captured, stored, or observed by a human being. The image exists only in the memory of the PD Meter and is immediately deleted after use.
In order to obtain the distance between any two points of an image, the scale of that image must first be determined.
A simple and practical way to do this is with an object of known scale. If an image with the known object is taken with the known object at the same distance from the camera as the target object (in this case, your eyes) a scale of measure can be obtained.
In the case of the PupilMeter, a standardized object is used for scale reference: a credit card.
Since all credit cards are manufactured with strict dimensions as per ISO/IEC 7810 (https://en.wikipedia.org/wiki/ISO/IEC_7810) and because they are owned by nearly everyone, this is the object used by the PupilMeter.