As we age, our eyesight changes. One important change is that the muscles controlling our pupils weaken. This can result in poor pupillary distance (PD) measurements during eye exams, and inaccurate PD measurements can lead to poor vision.
What is Pupillary Distance?
Pupillary Distance (PD) is the distance between the centers of your pupils. It is measured in millimeters (mm). As we age, our pupils get smaller and our PD changes. It is important to have your PD measured by an optometrist every two years so that your glasses or contact lenses can be adjusted accordingly.
How is Pupillary Distance Measured?
There are two main ways to measure pupillary distance.
The Ruler Method
This is the most common way to measure PD. You will need someone to help you with this method. First, you will need to find a ruler that is at least six inches long. Next, hold the ruler horizontally in front of your face, so that it is level with your eyes. Have your helper look through the ruler and line up the one-inch mark with the center of one of your pupils. Once they have done this, they should hold the ruler in place while you move your head until you can see the one-inch mark lined up with the center of your other pupil. Once both pupils are lined up, take note of where the six-inch mark on the ruler is located. This will be your PD measurement.
The Mirror Method
This method can be done by yourself and does not require a helper. First, find a mirror that is at least six inches wide and eight inches tall (a bathroom mirror works well for this). Place the mirror in front of you so that it is level with your eyes and about eight inches away from your face (you may need to adjust how far away from your face the mirror is depending on how big or small it is). Next, look into the mirror and locate each of your pupils in its reflection. Once you have found them, use a pen or pencil to draw a dot on each pupil’s reflection (this will help you keep track of where they are). Finally, move your head until both dots are lined up evenly in front of the four-inch mark.
The Importance of Accurate Measurements
As we age, our pupils get smaller, and our PD changes. It is important to have your PD measured every two years so that your glasses or contact lenses can be adjusted accordingly.
- If your PD measurements are off, your glasses or contact lenses will not be able to correct your vision properly.
- Accurate PD measurements can help to prevent eye strain and headaches.
- You may be at a higher risk for developing cataracts or glaucoma if your PD measurements are inaccurate.