What is Pupillary Distance?
Pupillary Distance (PD) is the measurement of the distance between the centers of your pupils. It is an important measurement used in the creation of eyeglasses to ensure that the optical centers of the lenses align properly with your eyes. A precise PD measurement helps optimize the visual performance and comfort of your glasses.
The average adult PD ranges from 54 to 74 millimeters, while children typically have PD measurements between 43 and 58 millimeters.
Your eye care professional usually includes your PD measurement in your prescription, but if it's not provided, you can measure it yourself using simple techniques or seek assistance from an optician.
How to Measure Your PD
Eye doctors should list your PD when they fill out a prescription for you, but sometimes they don’t. No worries, if it’s not there, you can still measure your pupillary distance at home.
If you're using our PD ruler on someone else (or they're using it on you), fold it to the side that says “Using a friend.” Have them sit down and focus on something 10 to 20 feet ahead to keep their eyes steady.
Next, place the PD ruler against their forehead and align the zero with the center of their right pupil. The number above the center of their left pupil is their PD. When measuring, it may help to close one of your eyes so you can read the precise number.
How to Measure PD by Yourself
Measuring your pupillary distance is a simple process, even if you're doing it alone. All you need is our PD ruler and a mirror. To ensure accuracy, it's recommended to relax and repeat the measurement a few times. If you get slightly different numbers, calculate the average by adding all the measurements together and dividing by the total number of measurements.
If you require progressive or bifocal lenses, measuring your near focus PD will also be necessary. For this measurement, you'll need someone else to assist you. The person measuring should follow the same instructions as before, but instead of focusing on a distant object, you'll both focus on a pen held between you. The measurer can then read and record your near focus PD.
By following these steps, you can obtain accurate pupillary distance measurements for a properly fitted pair of eyeglasses:
1. Fold the ruler and use the side that says "Using a mirror."
2. Stand about 8 inches away from a mirror and hold the ruler horizontally over your eyes. Align the zero mark directly over your left pupil, and you can stabilize it against your forehead if necessary.
3. Cover or close your left eye, and note the number directly above your right pupil. This is your pupillary distance.
How Do You Calculate Near PD For Reading Glasses?
You can calculate Near PD for reading glasses by subtracting 3mm from your distance PD. For example, if your distance PD is 63mm, then your near PD is 60mm.
If you are using Dual PD to calculate near PD, then subtract 1.5mm from each eye’s measurement. For example, if your dual PD is 33/31mm then your near PD would be 31.5/29.5mm.
Why PD Is Important!
Every set of prescription lenses has an “optical center,” which is determined by pupillary distance. Pupillary distance is used to determine where you look through the lens of your glasses and should be as accurate as possible.
Single vs. Dual PD
Single pupillary distance is the measurement between the center of one pupil to the center of the other. Dual PD is the distance between the center of each pupil to the middle of the nose. The two numbers in a dual PD represent each of those distances, with the right eye’s PD appearing first.
Tips When a Friend is Measuring
Have them crouch/sit while you stand so they are out of your field of vision.
Keep your eyes as still as possible.
Look above his/her head at something approximately 10-20 ft. away.
Do not look at the person measuring!
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