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Single PD vs. Dual PD | A Detailed Comparison


Have you ever heard of a single or dual pupillary distance (PD) number? If not, it is the distance between the very middle of each of your pupils and the bridge of your nose. It is measured in millimeters in one of two ways, from each pupil individually or together between the center of both pupils.

You might be wondering why you would need to know this number at all. The PD measurement is crucial because it helps in making your glasses. You want to have the prescription power of your new lenses right in the center of your vision. If this measurement is wrong, your glasses will be off-center, and you won’t be able to see out of them. It sounds like a pretty important detail, right?

Why Does My Eye Prescription Have Two PD Numbers?


The prescription that your optometrist gives you may or may not have the PD numbers included on it. If it is included, it can be one or two numbers.

A single PD number (also called binocular PD) is the total distance between the middle of both your pupils added together. A dual or two PD numbers (called monocular PD) is the measurement of the center of each pupil to the bridge of your nose individually.

Single PD vs. Dual PD


So, is it better to have a single or dual PD number when purchasing your new glasses? Is one more accurate than the other? 

Our eyes are not equally proportioned or symmetrical. One pupil could be a little further away from the bridge of your nose than the other pupil. Because of this, a dual PD is usually recommended. When you have each pupil-to-nose bridge measured individually, you’ll be sure to get your prescription right where you need them to be on your lenses. This can be especially important if you are considering progressive lenses or bifocals.

Does PD Have to Be Exact?


It is essential to be as exact as possible when measuring your pupillary distance for a new set of eyeglasses. If it isn’t precise as possible, your glasses will be made wrong by the lens maker, and you won’t be able to see out of them correctly. 

If you are unsure about your single or dual PD measurement, make it a point to get a good reading before spending the money on new specs. You’ll be glad you got it right the first time!

For more information on your pupillary distance (PD) numbers, schedule an eye exam. To learn more about healthy vision habits, schedule an appointment today.

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