reading glasses Pupillary Distance
Understanding Pupillary Distance (PD) for Your Reading Glasses
When you order a new pair of reading glasses, you'll likely come across a measurement called Pupillary Distance, or PD. While it might seem like a minor detail, getting this number right is essential for comfortable and clear vision. Let's explore why PD is so important for your readers and how you can find yours.
What is Pupillary Distance and Why Does It Matter?
Pupillary Distance is simply the distance in millimeters between the centers of your pupils. This measurement tells the lens maker where to place the optical center of each lens in your frames. When this optical center aligns perfectly with your pupil, you get the sharpest vision.
For reading glasses, an accurate PD is crucial. When you read, your eyes converge, meaning they turn slightly inward to focus on the text up close. Because of this, your PD for reading is slightly narrower than your distance PD (the one used for seeing things far away). If the lenses aren't centered correctly for this near focus, you might experience eye strain, headaches, or blurry vision. An incorrect PD can make your glasses feel "off" and uncomfortable to use.
How to Determine Your Reading PD
Finding your reading PD is a straightforward process. The general rule is to subtract 3mm from your distance PD.
- For a single (total) PD: If your distance PD is 63mm, your reading PD would be 60mm (63 - 3 = 60).
- For a dual PD: If your distance PD is written as two numbers, like 32/31, you would subtract 1.5mm from each number. Your reading PD would be 30.5/29.5.
This adjustment accounts for the natural convergence of your eyes when you look at something close up, ensuring your lenses are perfectly aligned for reading.
Measuring Your PD at Home
While getting your PD from an eye care professional is always the best option, you can get a good estimate at home. Here are a couple of methods:
1. The Ruler and Mirror Method
- Stand about 8 inches away from a mirror.
- Hold a millimeter ruler straight against your brow.
- Close your right eye and align the 0mm mark of the ruler with the center of your left pupil.
- Without moving the ruler, close your left eye and open your right.
- Read the measurement at the center of your right pupil. This number is your distance PD. Remember to subtract 3mm to get your reading PD.
2. Use an App
There are many smartphone apps designed to measure your PD. These apps typically use your phone's camera to take a precise measurement. They can be a convenient and often accurate way to find your PD without leaving home.
Why an Optician's Measurement is Best
Although home measurements can be helpful, we always recommend getting your PD measured by an optician. An expert has the proper tools and training to get the most precise measurement possible.
This is especially important if you have a strong prescription or require progressive or bifocal lenses. Small inaccuracies in PD can have a much larger impact with higher-powered lenses, so professional precision is key to getting a pair of glasses that works perfectly for you.
By ensuring you have the correct PD, you're taking an important step toward a comfortable and effective pair of reading glasses that will serve you well.