By Danielle Crull, ABOM
If there’s one thing I know about kids, it’s that simply telling them to do something doesn’t mean they will. With kids, we need to provide a source of reward for doing what we need them to do. Taking crucial measurements like the basic pupillary distance can be challenging even for a well-experienced optician. Babies and toddlers often do not understand our verbal commands, and preschoolers get distracted easily and many times are even fearful of our request. This requires us to abandon all our traditional methods and look for a creative approach.
With an adult, we simply ask them to look inside the pupillometer, measure their pupillary reflexes and (tada!) both monocular and binocular PDs are taken. If you don’t use a pupillometer, the handy-dandy PD stick will do, but not without asking the patient to follow your finger. Following your boring finger is like complex algebra for a 3 year-old. They might follow it in one direction, but completely lose track and become distracted with just about anything else that’s around. That’s not even to mention their “ants in the pants.”
Below are a few ways that you can be creative in getting a pupillary distance measurement on a little one.
- The fail-safe canthus to canthus measurement: Measure from the inner canthus of one eye to the outer canthus of the other. This is an adequate estimation, which should only be done if your patient refuses to open their eyes.
- Use a Window Ruler: For the toddler, the main objection to a traditional ruler is how it blocks vision. When you use a window ruler, the child will be able to see unobstructedly. Center the ruler on the bridge of the nose and use a close fixation. It could be you with a sticker on your nose, or a toy you are holding up. Make sure to occlude one eye and then the other, taking a monocular PD for each eye. I generally hold my thumb over the window of the eye I want to occlude. It’s crucial to occlude one eye at a time so you can account for a possible eye turn. Children with uncorrected esophoria or exophoria may exhibit an eye turn if both eyes are open and attempting to focus. A simple fix is to occlude one eye at a time and wait for the unoccluded eye to straighten out. When taking this type of measurement you are actually taking a near PD, so it’s important to add 1mm to each eye to calculate a distance PD.
- Use the demo lenses: Take a ruler and mark some distances on the demo lenses. Find the center of the bridge and begin measuring out every 2 mm and place a mark on the lens. It’s helpful to use different color markers. Get in front of the child and either take the near PD like mentioned above and add 1mm per eye or have something in the distance for the child to look at just slightly above your head. This is where it can be helpful to plan ahead. If you don’t already have a fixation tool (something like a lighted toy or poster) you need to think about where the best place is to put one in your dispensary. Then make a note as to which dot (or space between the dots ) marks the child’s pupillary distance. Don’t forget to do a quick occlusion test by covering one of their eyes at a time.
Image courtesy of Danielle Crull - Combining 2 and 3: Make demo lenses out of your window PD rulers. I have a couple of pairs of glasses in my office with the window rulers inserted at the correct distances. It’s useful to have one made for an infant-size head and another for a preschooler size. Or if making demo lenses isn’t something your office can do, then set aside a few pairs of glasses with the demo lenses pre-marked. This will save time when your patient is in and, as you know, two minutes is like two hours to a two year-old.
Image courtesy of Danielle Crull
