What is Pupillary Distance (PD)?
Pupillary distance (PD) measures the distance between the centers of your pupils. This measurement is used to determine where you look through the lens of your glasses and should be as accurate as possible. The average adult’s PD is between 54-74 mm; kids' are between 43-58 mm. Your eye doctor will usually measure your PD during an eye exam. However, if it was not given to you, you can measure it by yourself.
Why measuring your Pupillary Distance (PD) is important?
Every set of the prescription lens has an “optical center,” which is determined by pupillary distance. Pupillary distance is used to determine where you look through the lens of your glasses and should be as accurate as possible.
How then do we measure the Pupillary Distance (PD)?
Your prescription may tell you your PD. But if the PD is not available, use your friend or a mirror to help you figure it out..
Measuring Your Own PD
Position yourself approximately 8 inches (20cm) away from a mirror or yourself arm’s length from your friend.
Close your left eye and align the ruler’s zero to the center of your right pupil.
Try not to move your head or the ruler. Close your right eye and note the reading directly over your left pupil. That will be your PD.
you also need to measure the distance from two pupils to the center of nose respectively to make sure that if you have two PDs(OD & OS).
Having A Friend To Help You Measure
Look straight ahead with both eyes open facing your friend. Let your friend hold the ruler up to your right so the zero end lines up with your pupil.
Measure the distance from your right to your left pupil. The number that lines up with your left pupil is your PD.
Write the result down. To be certain of the result, let your friend measure a few more times to make sure your measurement is accurate.
Let your friend repeat the process on your left eye by measuring the distance from your left pupil to your right. Use the number that lines up with your right pupil. That's your PD. Write the result down. Repeat the process again to make sure the measurement is right.
What Is Single Vs Dual PD?
SINGLE PD is the pupillary distance between the center 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 centers 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).
How Do You Calculate Near PD For Reading Glasses?
You can calculate Near PD for reading glasses by subtracting 3mm from your distance PD. For example, if your distance PD is 63mm, then your near PD is 60mm.
If you are using Dual PD to calculate near PD, then subtract 1.5mm from each eye’s measurement. For example, if your dual PD is 33/31mm then your near PD would be 31.5/29.5mm.