What is Pupillary Distance, and Why Does It Matter?

Pupillary distance (PD) describes the distance between your pupils. This measurement is essential for getting the right pair of glasses, as it affects their fit and comfort, your vision clarity, and how the lenses align with your eyes. 

If you’re wondering about the mysterious PD number on your prescription, keep reading to learn what pupillary distance is, why it matters, how to measure it, and the risks of it being wrong. 

What Is Pupillary Distance (PD)?

There’s two types of pupillary distance: single and dual. Single PD is often used for single-vision glasses and measures distance between the centers of your pupils in millimeters. Since everyone’s face is different, this number is important for aligning lenses correctly with your eyes. 

For adults, the pupillary distance is typically between 54 and 74 millimeters. Children’s PD is shorter, usually between 43 and 58 millimeters. 

Dual PD consists of two numbers — one for each eye. Typically used for progressive or multifocal lenses, it measures each eye’s distance from the center of the nose bridge. This number may be the same for each eye, or it may be slightly different. 

Why Is PD Important?

You may be thinking, Millimeters are so small. Will a measurement that’s off by just a few millimeters actually make a difference? Well, the answer is yes! A correct pupillary distance measurement ensures that the lenses are centered and that vision correction is optimal. It affects how natural and comfortable your glasses feel.

PD is especially critical for progressive, multifocal, and high-index lenses, which rely on correct alignment to correct your vision. If it’s off, even by a little bit, it can cause headaches, eye strain, and blurred vision. 

How to Measure Pupillary Distance

Eye doctors and opticians typically measure pupillary distance during eye exams. This is the most accurate option, as they have specialized equipment and training. However, it’s not always included on your prescription, so if you’re buying glasses online, you may not have all the information you need to place an order. 

Luckily, you can also measure your PD at home by following these steps:

1. Stand in front of a mirror. 
2. Grab a ruler and identify which side measures millimeters and which measures inches. 
3. Hold the ruler in line with your pupils, centimeter-side up, and measure the distance between the centers of your pupils. For dual PD, measure the distance between the center of each pupil and the nose bridge.
4. Calculate your PD. Each of the tiny marks on the ruler is a millimeter, and there are 10 of them per centimeter. So if the measurement is two ticks past 5 centimeters, that means your pupillary distance is 52. 

There are also mobile apps and digital tools designed to measure pupillary distance. 

If you measure your PD at home, it’s a good idea to take a few measurements throughout the day and find the average. Your PD can change slightly based on light conditions and how dilated your eyes are, and finding the average can account for any variations in measurement methods. 

What Happens If Your PD Is Wrong?

Now that you know why pupillary distance matters, you can probably guess what can happen if the measurements are wrong. Because the lenses don’t align correctly with your eyes, you may experience blurred or distorted vision, eye strain and fatigue, and difficulty adjusting to your new glasses.

An accurate pupillary distance measurement is especially important with stronger prescriptions, bifocals, progressive lenses, and high-index lenses. If the measurement is off, even by a little bit, your glasses won’t have the intended effect.

Frequently Asked Questions

Can I Find My PD on My Prescription?

Some eye doctors include PD as part of your prescription, while others don’t. You may have to have it measured when you purchase your glasses. 

Do I Need to Re-Measure PD Every Time I Get New Glasses?

Adults’ PD doesn’t typically change; however, it’s a good idea to measure again just in case. Children who are still growing should measure their PD every time they get new glasses or lenses. 

Is It Okay to Estimate PD?

No, it’s not advisable to estimate your PD. Exact measurements are crucial for optimal vision correction.

Find the Perfect Glasses for You at Wolcott Optical

At Wolcott Optical, we’re dedicated to helping you find the perfect pair of glasses. From fit to lens shape to pupillary distance, we’ll ensure your glasses are right for you. Come visit our store in Salt Lake City, Utah, today!