How To Measure Your Pupillary Distance (PD)
Are you ordering a pair of prescription glasses online? If so, measuring your pupillary distance (PD) is crucial for ensuring the best vision correction. This guide will explain how to measure your PD without professional assistance.
Pupillary distance (PD) is the distance between the centers of your pupils. It determines the exact point of focus through your glasses, so it needs to be measured accurately.
The average PD for adults ranges from 54 to 74 mm, while for children, it is typically between 43 and 58 mm.
If you don’t have your PD from your optician and are ordering glasses online, you’ll need to measure it yourself.
Why Is Your Pupillary Distance Important?
Your pupillary distance (PD) is crucial for the accuracy of prescription lenses. Each pair of prescription lenses has an "optical center," which must align with your unique PD for optimal vision correction. Without this precise measurement, the effectiveness of your lenses may be compromised.
This measurement is also essential for blue light prescription glasses, designed to reduce the blue light emitted by computer screens and other devices. Proper PD measurement helps ensure these glasses effectively mitigate issues such as:
- Headaches
- Dry eyes
- Eye fatigue
- Blurred vision
- Insomnia
Blue light glasses are highly recommended for anyone who spends extended periods in front of screens, as they can significantly improve visual comfort and reduce related discomforts.
How to Measure Your Pupillary Distance
To measure your pupillary distance (PD), you will need a mirror and a ruler. Follow these steps:
- Position Yourself: Stand about 30 cm (12 inches) away from the mirror.
- Align the Ruler: Look directly at your mirror image and hold the ruler against your eyebrows.
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Measure:
- Close your right eye and align the 0 mm mark on the ruler with the center of your left pupil.
- Open your right eye and close your left eye. The PD measurement is the distance from the 0 mm mark to the center of your right pupil. This measurement should fall within the average range mentioned earlier.
Is This the Process for All Glasses?
For reading glasses, the process is similar. However, subtract 3 mm from your PD measurement to calculate the correct distance for reading glasses.
Measuring Another Person’s PD
If you need to help someone measure their pupillary distance (PD), such as a child, follow these steps:
- Position the Person: Have them focus on an object about 20 feet away, keeping both eyes open.
- Align the Ruler: Line up the 0 mm mark on the ruler with the center of one pupil. Then measure the distance to the center of the other pupil.
- Maintain Proper Position: Ensure you stay out of their line of sight. They should keep their gaze fixed straight ahead and avoid looking at you during the measurement. You can crouch or sit to stay out of their field of vision.
It’s a good idea to repeat the measurement several times to ensure accuracy and consistency. If done correctly, the process should yield a reliable PD measurement.
What Is Dual PD?
Some prescriptions require a dual PD, also known as monocular PD. This involves two measurements: one for each eye. Each number represents the distance from the center of the pupil to the bridge of the nose and is typically written in a format like 30/32. The first number refers to the right eye, while the second number refers to the left eye.
To measure dual PD, follow the same process as you would for a typical PD, but measure from each pupil to the bridge of the nose separately.
For reading glasses, you should subtract 1.5 mm from each measurement. For example, if your dual PD is 32/30, your adjusted PD for reading glasses would be 30.5/28.5.
We hope this guide helps you understand how to measure your PD accurately. For the most precise measurement, consider booking an appointment with an optician.
