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What is Pupillary Distance (PD) on a Prescription?

Pupillary distance (PD) is the distance between the centers of the pupils of the eyes, measured in millimeters. It is a crucial measurement in eyeglass fitting and is often required for ordering prescription eyewear. In this blog post, we will explore what pupillary distance is, how it is measured, and why it is important. If you're curious what the other information on your eyeglasses prescription means, checkout our blog on how to read an eyeglasses prescription!

What is Pupillary Distance (PD)?

The pupillary distance is the distance between the center of one pupil to the center of the other pupil. This distance is important because it affects the way light enters the eyes and how it is focused. Correctly measuring the PD ensures that prescription eyewear is accurately centered over the eyes, allowing the eyes to focus properly.

How is Pupillary Distance Measured?

There are several methods for measuring pupillary distance, but the most common and accurate method is by using a pupillometer. A pupillometer is a specialized tool that uses a ruler or a digital screen to measure the distance between the pupils accurately.

Another method of measuring PD is by using a mirror and a ruler. The person being measured stands about 8 inches away from a mirror, and a ruler is held horizontally against the bridge of their nose. The person closes one eye, and the other eye looks straight ahead. The measurement is taken from the center of the pupil in the open eye to the bridge of the nose. The process is repeated with the other eye, and the measurements are added together to get the total PD.

Why is Pupillary Distance Important?

Pupillary distance is crucial in ensuring that prescription eyewear is correctly centered over the eyes. Correctly positioned lenses prevent eye strain and allow for the most effective correction of refractive errors like nearsightedness, farsightedness, and astigmatism.

Wearing eyeglasses with the wrong PD can cause visual distortions, headaches, and eye strain. These symptoms can be particularly problematic for those who wear progressive lenses, which require precise PD measurements to ensure that the right area of the lens is being used for the right distance.

Pupillary distance is a critical measurement in eyeglass fitting, and it is important to have it accurately measured when ordering prescription eyewear. By ensuring that the PD is correctly measured, eyeglass wearers can avoid visual distortions, headaches, and eye strain, and get the best possible vision correction.


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