It might seem like getting glasses ordered should be a snap. You pick out your frames and you’re all done! While opticians work behind the scenes to make it seem easy, there are actually many measurements and calculations that go into a quality pair of eyewear.
Your visual experience can be horrible if certain measurements aren’t taken. Different lens styles require different things, but one measurement is standard for all eyewear - the pupillary distance. This one set of numbers is essential for your vision to be crisp and clear. So what exactly is it? Let’s learn more!
All Faces Aren’t Symmetrical
This comes as a shock to some people, but most people’s faces are asymmetrical. This means a special tool, called a pupillometer, is required to measure your pupillary distance. Called PD for short, this measures the distance from the middle of your nose bridge out to the center of each pupil. Most of the time, your optician will end up with two separate numbers; one for the left side and one for the right.
While it’s not impossible, most people’s PD is different between each eye. Some optical manufacturers prefer to use the PD as one number, and in that case you would combine the two numbers. However, to be more accurate in accounting for facial anomalies, using a two number method is typically preferred.
How And When To Measure
Children should absolutely be measured every time they order a new pair of glasses, as their PD can change as their head grows. Once you’ve reached adulthood, your PD will remain the same and most of the time remeasurements aren’t necessary.
Sometimes you’ll see a PD measured with a ruler, but the pupillometer mentioned above is a more accurate method. This handheld machine is placed up against your nose and brow like you’re looking through binoculars. You’ll see a light on the inside and it’s your job to look straight at it.
The optician will be on the other side moving two slides back and forth until a vertical marking lines up with the reflected light they see on your pupils. It’s really that easy!
Your PD Matters
If your eye doctor hasn’t included your PD measurement on your eyeglass prescription, be sure to ask for it. It’s hard to take it yourself, so leave it to the professionals. Remember, an accurate pupillary distance is important for the best vision through your glasses.