PD stands for pupillary distance. It’s one of the most important measurements used when making glasses, yet it’s often misunderstood or overlooked. If you’re ordering glasses online, PD plays a direct role in how clear and comfortable your vision feels once you put them on.
This guide explains what PD is, why it matters, and what happens if it’s wrong.
What PD means
PD is the distance between the centre of your pupils, measured in millimetres. It tells the lab exactly where to position the optical centre of each lens so it lines up with your eyes.
Everyone’s PD is different. Even small differences matter because lenses are designed to work best when your eyes look through the correct point.
Why PD matters for clear vision
Lenses are strongest at their optical centre. If that centre doesn’t line up with your pupils, your eyes are forced to compensate. This can affect clarity, comfort, and how your glasses feel throughout the day.
When PD is correct, vision feels natural. When it’s off, even by a few millimetres, glasses can feel uncomfortable or slightly “wrong,” especially when worn for long periods.
What can happen if PD is incorrect
Incorrect PD doesn’t usually make glasses unusable straight away, but it can cause issues over time.
Common problems include:
- Eye strain or headaches
- Difficulty focusing
- Blurred vision at certain angles
- Feeling dizzy or fatigued when wearing glasses
These issues are more noticeable with stronger prescriptions, but PD matters at all prescription levels.
Is PD always on your prescription?
In many cases, PD is not written on a standard eye test prescription. This doesn’t mean it isn’t important. It simply means it’s often measured separately or provided when glasses are dispensed in person.
When ordering online, PD is usually entered during the checkout or lens selection process. This allows the lenses to be positioned correctly for you.
Single PD vs dual PD
Some people have a single PD measurement, while others have two values, one for each eye. This is known as dual PD.
Dual PD accounts for the fact that pupils are not always perfectly centred. Using dual PD allows for more precise lens placement, which can improve comfort and accuracy, particularly for higher prescriptions.
Why PD is especially important when buying glasses online
When you buy glasses in-store, PD is usually measured and applied automatically. Online, the process is different. You are either asked to enter your PD manually or it is measured using digital tools.
This step replaces what would normally happen in person, which is why accuracy matters. A correct PD helps ensure the glasses you receive feel natural from the moment you put them on.
How PD affects different types of glasses
PD plays a role in all prescription glasses, but it becomes more critical as prescriptions become stronger or more complex. Varifocal and higher prescriptions rely heavily on accurate alignment to work properly.
Even with standard single vision glasses, correct PD helps reduce eye strain and improves overall comfort.
Final thoughts
PD is not just a technical detail. It’s a key part of how glasses work. If you’re ordering glasses online, taking the time to get your PD right helps ensure your glasses feel clear, comfortable, and easy to wear.
When PD is correct, glasses fade into the background. When it’s wrong, you notice.
FAQ – What PD Is and Why It Matters
What does PD stand for in glasses?
PD stands for pupillary distance. It is the distance between the centres of your pupils, measured in millimetres.
Why is PD important when ordering glasses online?
PD tells the lab where to position the optical centre of each lens. If it’s wrong, vision can feel uncomfortable or strained.
What happens if my PD is slightly wrong?
Small errors can cause eye strain, headaches, or blurred vision, especially with stronger prescriptions.
Is PD always included on my prescription?
No. Many eye test prescriptions do not include PD. It is often measured separately when glasses are dispensed.
What is the difference between single PD and dual PD?
Single PD is one measurement for both eyes. Dual PD uses a separate measurement for each eye, allowing more precise lens placement.
Does PD matter for all types of glasses?
Yes. PD affects all prescription glasses, but it becomes more important for higher or more complex prescriptions.
