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Accuracy and Repeatability of Self-Measurement of Interpupillary Distance

McMahon, Timothy T.*; Irving, Elizabeth L.; Lee, Claudia

doi: 10.1097/OPX.0b013e318257f37b
Original Articles

Purpose. To determine the accuracy and repeatability of participants determining their own interpupillary distance (PD).

Methods. Fifty-two healthy and naïve participants were enrolled and analyzed. All participants analyzed were without strabismus. Participants had PD measurements taken by a trained examiner using both a PD rule and an optical pupillometer. Participants then, following online instructions measured their own PD in a mirror, measured a friend's PD and used an online application downloaded to an IPod. Measurements were repeated twice for each type, and the pupillometer results were considered the gold standard (referent).

Results. The mean difference between the examiner PD rule measurement and the pupillometer were +0.59 mm [95% limits of agreement (LoA) −0.69 to +1.88], pupillometer-self +0.46 mm (−5.22 to +6.14), pupillometer-friend +2.00 mm (−3.80 to +7.81), and pupillometer-App −3.24 mm (−3.09 to +9.57). Measurements of repeatability using the 95% LoA for the examiner are −0.79 to 0.73 mm for the pupillometer and −1.04 to +1.20 mm for the PD rule. Participants' repeatability for the self-measurement (mirror) was −3.61 to +4.75 mm, employing a friend was −3.74 to +3.94 mm, and using the IPod application was −6.63 to +6.51 mm.

Conclusions. Participants' ability to measure their own PD using techniques and applications available via the Internet result in poor accuracy and poor repeatability.



Department of Ophthalmology and Visual Sciences, University of Illinois College of Medicine, Chicago, Illinois (TTM), and School of Optometry and Vision Science, University of Waterloo, Waterloo, Ontario, Canada (EI, CL).

Received November 17, 2011; accepted February 22, 2012.

Timothy T. McMahon Department of Ophthalmology and Visual Sciences University of Illinois College of Medicine 1855 West Taylor Street (M/C 648) Chicago, Illinois 60612 e-mail:

© 2012 American Academy of Optometry