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Monocular PD (Pupillary Distance) is the measurement of the distance from the center of the bridge of the nose to the center of a single pupil. This measurement is taken separately for the right eye and the left eye. For example, a prescription might read 32 mm OD (Right) and 30 mm OS (Left).
read more about monocular pd ...Monocular PD is more accurate because very few faces are perfectly symmetrical. Measuring each eye separately accounts for any differences in the distance between the eyes and the nose. This individualized measurement helps make sure the optical center of the lens is positioned correctly for each eye.
The optician uses this precise measurement to position the optical center of each lens perfectly in the horizontal direction. Monocular PD ensures that the eye looks through the clearest part of the lens when looking straight ahead, reducing the risk of prismatic effect and visual fatigue.
An incorrect PD, even by a few millimeters, forces the eyes to compensate for the misalignment. This compensation can cause eye strain, double vision, and headaches, making the new glasses unusable until the lenses are remade correctly.
Precision is important for your backup glasses. Since contact lenses eliminate PD measurement issues by centering naturally, your glasses must be equally precise. Correct monocular PD guarantees stable, comfortable vision the moment you switch from contacts to glasses.
Binocular PD is one measurement for both eyes combined (e.g., 62 mm). Monocular PD is two separate measurements for the right eye and the left eye (e.g., 31 mm / 31 mm).
No, monocular PD is a measurement only for glasses because contact lenses float directly on the tear film and center themselves on the pupil.
Yes, PD measurement rarely changes in adults and can usually be used for new glasses, but it should always be verified by an optician.
Always request a monocular PD measurement for progressive lenses. Most human faces are slightly asymmetrical; using a binocular PD can result in one eye being misaligned with the progressive corridor, causing significant blur and disorientation.
National Eye Institute. Healthy Vision Tips (nei.nih.gov). 2024.
Mayo Clinic. Understanding Your Eyeglass Prescription (mayoclinic.org). 2023.
All About Vision. Measuring Pupillary Distance (allaboutvision.com). 2024.
Review of Optometry. Errors in PD Measurement (reviewofoptometry.com). 2024.