If you haven't ordered prescription eyeglasses online before, you may have some questions, especially when you come across terms like pupillary distance. This article will teach you everything you need to know about PD.
What is Pupillary Distance (PD)?
Pupillary distance, sometimes referred to as pupil distance or just PD, is the distance between the center of each pupil and the bridge of your nose, measured in millimeters. Pupillary distance is essential for crafting prescription glasses because it helps us know where to place the power on your lenses. Without a correct measurement, the prescription power of your lenses will be off-center from your eyes and you won't be able to see out of your glasses, even if your prescription is otherwise correct.
Where can I find my Pupillary Distance?
Two ways:
- You can obtain it from your optometrist
- You can measure it using our special ruler, following the steps here: (link to How to measure PD)
Each time you received an eye exam or purchased glasses in person, they measured your PD to craft your lenses. This measurement, however, isn't always included on the print-out prescription you receive after an eye exam. If you want to order eyeglasses online, but don't have your PD, call your optometrist to ask for it.
If obtaining your PD measurement from your optometrist isn't possible, you can measure it from home using our special ruler, and following the steps here: (link to How to measure PD)
Can I just guess my PD?
Do not guess your pupillary distance then order prescription glasses!
The pupillary distance must be accurate for prescription glasses to work properly. Think of it like guessing your shoe size: If you buy with a pair of shoes with the wrong size measurement, you will have trouble walking. The same principle applies here. Guessing your PD will result in you not being able to see out of your prescription glasses properly and you will have to order a new pair with the correct pupillary distance.
What do Monocular and Binocular mean? What is single and dual PD?
They are non-scientific terms for the following:
Monocular PD, sometimes referred to as dual PD, measures the center of each pupil to the bridge of the nose.
Binocular PD, sometimes referred to as single PD, is total distance between the center of both pupils.
Which is more accurate: monocular or binocular PD?
We recommend measuring for monocular PD. This is why:
Our faces are usually not symmetrical. One eye may be a bit further from the bridge of the nose than the other. Your binocular PD may be 58.5mm total, but your monocular PD may be 27mm for their right eye and 31.5mm for their left. Monocular PD allows us to be as accurate as possible when crafting your lenses. This is especially important in the case of progressives—which are lenses that include prescriptions for both distance and reading.
What is the average pupillary distance?
A binocular PD of 50mm or lower is typical for a child. So if you get those values, we recommend you check your ruler and methods then measure again!