last word: dispensing insights
PDs: Measure for Measure
By Karlen McLean, ABOC, NCLC
Often, the first dispensing tool any optician receives is a PD (Pupillary Distance) ruler. My first introduction to this tool and taking PD measurements was at lunchtime on my first day in optical about 35 years ago.
My boss slapped a PD ruler in my hand and said, “Here, use this to measure the distance between the centers of someone's pupils; and, if they need bifocals, measure from the bottom of the frame to 3mm below their lower lid for the height. I'll be back in an hour.”
The truth about PDs is that it really isn't that simple; and as the core lens measurement, incorrect PDs can negatively impact the success of the final lens products and result in remakes.
WHEN TO USE A PD RULER
The PD stick has its place when taking frame and seg height measurements (more in later columns), and maybe as a backup, but not for the best PD measurements. Sure, it's easy to whip out a PD ruler and do a quick measurement, but the stick can have more inaccuracies due to measurer-to-measuree differences (i.e., posture and gaze alignment) than a pupilometer even with a simple Rx's, healthy eyes, and compliant patients.
WHEN TO USE A PUPILOMETER
Corneal reflex pupilometers are more accurate than PD rulers for binocular and monocular PDs. They should be used when taking anyone other than an infant's PD.
Pupilometers should be used especially when measuring for multi-focal lenses and PALs, since they take monocular PDs more precisely.
A monocular PD is important to obtain because faces and eyes are usually not symmetrical; and, taking a separate PD for each eye ensures that the patient's line of sight will pass through the optical center of the lenses and no unwanted prism will be induced.
DISPENSING INSIGHT:
Take PD measurements using a pupilometer whenever patients order new lenses, no exceptions. EB
| Never Assume… |
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1 That true PDs are the same as patients' records shows. Previous error, injury, surgery, and aging result in PD changes, especially in kids and teens. 2 That the patients' PD are the same as their current eye-wear reads. Their actual PDs may be different than those in their everyday eyewear, and is probably different between everyday eyewear and task-specific eyewear. If the actual PD varies widely from the PD in their current eyewear, ask: “Are you happy with your vision using your current eyewear?” If not, you can choose to explain the PD difference and visual adjustment they may experience with their new eyewear if made “on PD.” 3 That because you've been taking PDs with a ruler for years, you're always accurate. Some opticians have this ability, but others don't. Measuring PDs using a ruler takes technique, while PDs utilizing a pupilometer are a procedure. |
| Senior editor Karlen McLean has been in the optical industry for 35 years. She has spent half of that time in the dispensary. In this monthly column, she will share her own experiences, and hope you'll share yours. Contact her via email at karlen.mclean@wolterskluwer.com |
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