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Educational content only
This page is general patient education, not medical advice. It does not diagnose conditions, recommend specific treatments for you, or replace a conversation with your eye care provider. Always consult a qualified clinician before making decisions about your eye health.
PD — the distance between your pupils — gets a single line on your prescription, but it determines whether your glasses actually deliver the prescription they're supposed to. For progressives, an error of 1-2mm can ruin the lens.
What to know
When PD matters — and how much.
Low-Rx readers
Off-the-shelf usually fine
Drugstore readers with low plus power and no astigmatism tolerate small PD errors. Your eyes can compensate. This is why $20 reader pairs work for many people.
Higher Rx, astigmatism
Accurate PD becomes essential
Stronger prescriptions and any significant cylinder (astigmatism correction) demand accurate PD. A 2-3mm error creates noticeable prismatic effect, eye strain, and sometimes double vision. Worth the in-person measurement.
Progressives
PD accuracy is critical
Progressive lenses have narrow corridors of clear vision. The reading zone at the bottom of the lens is small and precisely placed. A PD error of even 1.5mm can put the reading zone outside your line of sight when you look down, making the lens functionally useless for near work.
Near vs distance PD
Two measurements, sometimes both needed
Distance PD is measured looking at something 20+ feet away. Near PD is measured looking at reading distance — typically 2-4mm less than distance PD because your eyes converge inward when reading. Quality progressive fittings often use both measurements.
Ask for a remake if
Your new glasses make you feel dizzy, give you headaches that didn't exist before, cause double images, or make it difficult to read without tilting your head — even if the prescription is correct. PD errors are common and remediable. Reputable opticals stand behind their fittings.
Common questions
Honest answers to common questions.
Can I measure my own PD?+
Yes, with a mirror, ruler, and patience — or with the various apps and online tools. Home measurements are typically accurate within 1-2mm, which is fine for low-Rx single-vision glasses. For progressives, get it measured professionally.
Why isn't PD on my prescription?+
It often isn't — because PD is technically a fitting measurement, not a prescription element. Some doctors include it; many don't. You can request it specifically. Federal law (the Eyeglass Rule) requires your prescription, but doesn't always require PD. Always ask before ordering glasses online.
My PD is 'split' as 32/31 or 31.5/31.5 — what does that mean?+
That's individual PD for each eye, measured from the center of your nose to each pupil. Sometimes the eyes aren't symmetric. Modern fittings often use the split version because it's more accurate, especially for stronger prescriptions and progressives.
Does PD change as I age?+
Not after your skull stops growing — usually around age 18-20. Children's PD increases as they grow. An adult's PD is essentially fixed for life, which is why getting it measured once carefully gives you a useful number going forward.
Will an online retailer make a bad pair if my PD is slightly off?+
For mild single-vision Rx, probably not noticeably. For higher Rx or progressives, yes. Reputable online retailers will remake or refund — but the hassle of waiting and re-ordering is part of the cost of online buying. In-person fittings catch this before it ships.