Pupil distance

In the optical industry, there are sometimes highly technical terms. For example, you've probably already heard of pupillary distance. But what are they really?
Mymonture.com invites you to find out what pupil distances are, what they're used for, and how and why they're measured

What are pupillary distances?

Representing the distance between the centers of the two pupils, pupillary distance is measured in millimeters. It's made up of two half-distances, one from the bridge of the nose to the center of the right pupil, and the other from the bridge of the nose to the center of the left pupil. Generally speaking, this measurement remains the same almost throughout life, and ranges from 57 to 67mm for an adult.

Why do we need to measure them?

Every person is unique: so are their face, their eyes, and thus their measurements. To guarantee maximum visual comfort, the optical center of the lens must be perfectly aligned with the wearer's visual axis. Indeed, if the corrective lens is poorly centered, this can lead to accommodation difficulties, followed by migraines and visual fatigue. In the worst-case scenario, poor centering can lead to other visual problems such as myopia, presbyopia or hyperopia. This is why it's so important to adjust corrective lenses to suit the wearer's eyesight.
Corrective optical frames are as unique as the wearer themselves.

How do you measure them?

There are several ways of measuring your pupillary distance.

• You can ask your ophthalmologist directly, who, from August 19, 2014, will be obliged to indicate this value on the prescription he or she issues. Your ophthalmologist has particularly effective equipment for calculating your pupillary distance accurately.
• If you've already worn glasses, you can look at your previous prescription, where the pupillary distance will be annotated. This is often preceded by the words "OG" and "OD", meaning left eye and right eye respectively.
• You can also ask a qualified optician for more information. Your optician will be able to measure your pupillary distance, for example with a corneal reflection pupillometer.
• When you order online, you have two options. Firstly, if you've already worn glasses, you can send in your old frames directly. In this way, the optician will be able to determine your deviation, thanks to the measurements already taken.
  On the other hand, if you've never worn glasses before, you can send a photo of your face, taking care to place a small ruler (or tape measure) horizontally just above your eyes. If possible, place the "10" on the bridge of your nose, to facilitate measurement. This way, the optician will be able to calculate your pupillary distance without any problems. To make things even easier, you can ask friends and family to help you get the best shots. The clearer the photo, the more accurate the calculation, the more comfortable your vision will be.