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Guides and answers
Guides on measuring your pupillary distance, reading your prescription and ordering glasses online with confidence.
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Is Pupillary Distance the Same as Axis?
Is pupillary distance the same as axis? No — PD is in millimeters, axis in degrees. Why the two get confused on a prescription, and what a mix-up does.
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How to Measure Your Face for Glasses (Frame Width, Bridge & Lens Size)
Measure your face for glasses: the three numbers on every frame, taking them from an old pair or your face, which one decides the fit, and where PD fits.
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Should You Round Your PD Up or Down?
Should you round your PD up or down? What half a millimeter actually costs, from Prentice's rule, and why how you measured matters far more than rounding.
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Are Pupillary Distance Apps Accurate?
Are pupillary distance apps accurate? Peer-reviewed tests vs a clinical pupillometer, why older app studies did worse, and how apps compare with a ruler.
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Entering Your PD at Zenni, EyeBuyDirect, Warby Parker & LensCrafters
Entering your pupillary distance at Zenni, EyeBuyDirect, Warby Parker & LensCrafters: what each asks for, the formats they accept and what their tools do.
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Near PD vs Far PD: Why You Have Two Numbers
What far PD and near PD are, how much they differ, why a prescription sometimes shows two numbers, and which figure each kind of glasses needs.
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Does PD Matter? What a Wrong Pupillary Distance Does
Does pupillary distance matter? What happens when your PD is wrong, how the error interacts with prescription strength, and how accurate it needs to be.
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Where Is the PD on Your Glasses Prescription?
Where the pupillary distance (PD) is on your glasses prescription, why it's so often missing, what OD and OS mean, and what to do if it isn't there.
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Does Your Pupillary Distance Change?
Does your pupillary distance change with age or in adults? Why two measurements of one face can differ by several millimeters when nothing has changed.
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Average Pupillary Distance by Gender and Age
Average pupillary distance (PD) for glasses: 63.4 mm in 3,976 adults, 62.3 mm for women, 64.7 mm for men. What the spread means and why studies disagree.
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What Is Pupillary Distance (PD)?
What pupillary distance (PD) is, what the number means, how far, near and monocular PD differ, what's typical and what to do if your prescription lacks it.
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How to Measure Pupillary Distance for Glasses at Home (3 Methods)
Three reliable ways to measure your pupillary distance for glasses at home: a ruler and mirror, a friend, or your iPhone. Plus far, near and monocular PD.