ALL ABOUT PUPILLARY DISTANCE (PD)
WHAT IS PUPILLARY DISTANCE (PD)?
Pupillary distance, or PD is the measurement of distance in millimeter between the pupils. This information allows our opticians to place the optical center of the lenses directly in front of the pupils, allowing for the best vision possible. PD is often included on a prescription (see below) but if it isn’t, it is easy to measure for yourself or for a child.
HOW TO MEASURE PD ON YOUR OWN
METHOD 1: IF YOUR CHILD HAS GLASSES
METHOD 2: IF YOUR CHILD DOES NOT HAVE GLASSES
METHOD 3: IF YOUR CHILD HAS AN EYE MUSCLE IMBALANCE/STRABISMUS (SUCH AS ESOTROPIA OR EXOTROPIA)
METHOD 4: VISIT A LOCAL OPTICIAN
Most opticians will measure PD for free or a small fee. This method is the easiest for our youngest customers receiving their first pair of glasses. It is also the best method if you are ordering for a child with an eye muscle imbalance (also called Strabismus). However, Method 3 can be used for measuring PD for a child with Strabismus if you are unable to obtain the PD from your doctor. Make sure that your child’s pupils are facing forward when you take the measurement.
IF YOU HAVE A PAIR OF EXISTING GLASSES AND A NON-PERMANENT, FELT TIPPED MARKER.
1. Have your child put on their glasses.
2. Ask the child to cover one eye and look at an object that is at least 20 feet away. For example, they could sit inside and focus on a tree or building out the window.
3. Use the non-permanent marker to place a single dot on the lens over the center of the pupil.
4. Repeat this process with the other eye.
5. To double check this is done correctly: with both eyes open, the child should see the dots overlap when they are looking through their marked glasses at the distance object.
6. Remove the glasses and measure the distance between the two dots with a millimeter (mm) ruler.
IF YOU DO NOT HAVE A PAIR OF EXISTING GLASSES
1. Have your child look at an object that is at least 20 feet away. For example, they could sit inside and focus on a tree or building out the window.
2. Take a millimeter (mm) ruler and measure the distance from the center of one pupil to the center of the other pupil.
3. You can make this measure even more accurate by taking a flashlight and shining it in your child’s eyes. The reflection on the pupils will help you to find the center of the pupils. When doing this, make sure that the child continues to look at the distant object.
4. Whether you are using a flashlight or not, take this measurement at least 3 times to ensure that your measurements are consistent.
IF YOUR CHILD HAS AN EYE MUSCLE IMBALANCE/STRABISMUS AND YOU ARE UNABLE TO OBTAIN PD FROM YOUR DOCTOR
1. If your child’s eyes turn inward or outward when looking at distance, cover one eye and have them look at an object that is at least 20 feet away with the uncovered eye. For example, they could sit inside and focus on a tree or building out the window. It is important that the child’s pupils are facing forward when you take this measurement.
2. Take the measurement in millimeters from the center of the bridge of the nose to the center of the pupil.
3. By doubling this measurement, you will get an accurate measurement of the distance PD. You only need to take this measurement for one eye, not both.
WHERE TO FIND PD ON YOUR PRESCRIPTION
There are several ways Pupillary Distance, or PD, can be written on your prescription.
A single PD number is measured from pupil to pupil.
Average PD measurements for kids are between 41 and 53.
The second method results in two PD numbers (one for each eye) and is called a ‘Monocular PD’. This is a measurement from each pupil to the center of the face. Average measurements for kids are between 20 and 27.
A prescription can also have two PD numbers if one PD is for near/reading and another for far/distance. The PD for near/reading will typically be 3 mm less than the far/distance PD. Average PD measurements for kids are between 41 and 53.