What is single vs dual pupillary distance?
Understanding the difference between the two is simple and easy, and can be easily visualised through the images below.
SINGLE PD is the pupillary distance between the centre of one pupil to the other, which can be a distance PD or near PD. Distance PD can be used to order any type of prescription glasses except reading glasses. Read below to learn how to calculate near PD for reading glasses.
DUAL PD, or monocular PD, consists of two numbers and is the distance between the centres of each pupil to the bridge of the nose. Dual PD is usually written in the following notation: 32/30. The first number is always the right eye (OD) measurement, and the second number is the left eye (OS).
You can ask your eye doctor to include your PD measurement on your prescription, or if you don’t have it, you can use one of the following methods to measure it—it’s super easy!
All you’ll need is a pair of glasses, a felt tip marker and a ruler marked in millimetres!
With glasses on, focus on an object about 20 feet away from you or, if you’re near-sighted, on a close object.
Mark a dot over the object on your right lens. Do the same for the left lens.
Finally, take your ruler and measure the distance between the two dots. Align the 0 mm line with one dot. The second dot is your PD.
For this method, you’ll need a mirror, pencil and paper and a ruler marked in millimetres.
Position yourself approximately 8 inches (20 cm) away from a mirror.
As you look straight ahead into the mirror, position the ruler over the bridge of your nose.
Close your left eye and align the 0 mm over the center of your right pupil. Measure the distance from your right and left pupil. The number over your left pupil is your PD.
Friends make everything better, including calculating your PD! Make sure you have pencil and paper and a ruler marked in millimetres, too.
Position your friend out of your field of vision. Focus on an object from 10-20 feet away.
Have your friend align the 0 mm over the center of your right pupil.
Measure the distance from your right and left pupil. The distance between them is your PD.
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