Pupillary Distance (PD)
What is a PD and why is it necessary to make prescription lenses?
Your pupillary distance (PD) is the distance between the centers (pupils) of your eyes, measured in millimeters.
This measurement needed to properly align the prescription lenses to your line of sight. To optimize your vision, the prescription lens is cut so the center is directly in front of your pupil.
People have two different PDs, distance and reading. Distance is where your pupils are when focusing on an object 20 feet away. Reading is when you are focusing on something about 12-18 inches in front of you
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Ways that PD measurements are read
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There are two ways to measure a PD, from pupil to pupil which is called bi-nocular. The Binocular is usually within 10mm of 64mm.
The monocular PD is measured from the centerline of your nose to each pupil. The monocular is usually within 5mm of 31mm per eye.
Monocular PD's are preferred in multifocal, bifocal, trifocal, or progressive lens prescriptions.
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How to measure your own pupillary distance
Pupillary Distance (PD) is very simple to measure yourself or with the help of a friend. Any local optician can also provide you with this information.
Ask your friend to do the following:
1) Hold the ruler up to the bridge of your nose.
2) Have your friend close one eye.
3) Align the ruler's zero on the left, in the center of your pupil. The pupil is the black spot in the middle of the eye.
4) Without moving the ruler, have them move their head to the right and read the millimeter line corresponding to your other pupil.
5) Repeat the process two or three times for accuracy.
6) Record your results.
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