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What is PUPILLARY DISTANCE (PD)
Your pupillary distance (PD) is the distance between the center of each of your pupils. The pupil is the black hole in the center of your iris. The Iris is the colored, muscular ring around the perimeter of the pupil. Your PD is measured when you are looking straight ahead.
Your eyeglass frames should be aligned based on your PD. Optometrists use this measurement to create the correct prescription lenses, centering the clearest part of each lens directly in front of your pupil.Â
For example, if your PD measures 60mm, the center of the lenses should be placed 60mm apart in your frame. PD is especially important when your optometrist is fitting your glasses with progressive lenses; these require precise lens-to-pupil alignment to provide comfortable vision at all distances.Â
When your glasses are designed with your exact PD measurements in mind, they are comfortable and clear.
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There are two primary methods for measuring PD: binocular PD and monocular PD. Binocular PD is the measurement from pupil to pupil between each eye. Monocular PD is the measurement from the center of the bridge of your nose to the center of each pupil. Of the two measurements, monocular PD tends to be more accurate since the nose-to-pupil measurement may not be equidistant on both sides.
Though a professional can measure your PD for you during any eye exam, you can also measure the distance yourself. This can be helpful when you’re ordering glasses online and need precise measurements to get the right frames. Here are the three easiest ways to measure your own PD:
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Instructions
1. Stand about 8" from a well-lit mirror.
2. Close your right eye.
3. Align a millimeter ruler to the center of your left pupil across your brow bone.
4. Open your right eye.
5. Measure the distance to the center of your right pupil. This is your binocular PD.
6. To measure your monocular PD, measure the distance from each pupil to the center of the bridge of your nose. There will be 2 numbers. For example, if the distance from your right pupil to the bridge of your nose is 33 mm and the distance from your left pupil to the bridge of your nose is 31 mm, your monocular PD is 33/31.
Tips
• Make sure that the ruler measurements are in millimeters.
• Repeat this exercise 2-3 times for the best level of accuracy.
• Hold still; the result is more accurate when there is less movement.
Instructions
1. Put on your glasses. Have a felt tip marker handy!
2. Focus on an object at least 20 feet away.
3. Mark on your right lens directly over the object.
4. Mark over the object on your left lens.
5. With both eyes, make sure the markings overlap into a single dot.
6. Remove your glasses and measure the distance between the two dots with a millimeter ruler.
7. For a monocular PD, measure the distances from each dot to the center of the bridge of the frame.
Tips
• Make sure that the ruler measurements are in millimeters.
• Repeat this exercise 2-3 times for the best level of accuracy.
• Hold still; the result is more accurate when there is less movement.
• If you’re measuring for reading glasses, focus on a close object like a book or computer screen.
Instructions
1. Face your friend and look straight ahead with both eyes open.
2. Have your friend hold the ruler up to your right so the zero end lines up with the center of your pupil.
3. Measure the distance from the center of your right to the center of your left pupil. The number that lines up with your left pupil is your PD.
4. Have your friend repeat the process on your left eye by measuring the distance from your left pupil to your right. That's your PD.
5. To measure your monocular PD, have your friend measure the distance from each pupil to the center of the bridge of your nose.
Tips
• Make sure that the ruler measurements are in millimeters.
• Repeat this exercise 2-3 times for the best level of accuracy.
• Hold still; the result is more accurate when there is less movement.
The methods described above measure PD for distance lenses. You can calculate a near PD measurement for reading glasses by subtracting 3mm from your distance PD. For example, if your distance PD is 63mm, then your near PD is 60mm.
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If you are using Dual PD to calculate near PD, then subtract 1.5mm from each eye's measurement. For example, if your monocular PD is 33/31mm, then your near PD would be 31.5/29.5mm.
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