A Comparative Analysis of Interpupillary Distance Measurement Techniques Evaluation in Modern Times: From Rulers to Apps

Purpose: The use of mobile phone applications (apps) in the health sector, including in eye care, is increasing. This study aimed to compare interpupillary distance (IPD) measurements using common clinical techniques (pupillometer, PD ruler, and autorefractor), which are contact procedures, with measurements from a non-contact mobile phone application.

Methods: Forty participants were recruited (mean age 25.65±3.72 years, 21 male and 19 female). Binocular distance and near IPD measurements from four instruments were compared: pupillometer (TOPCON PD-5, Japan), PD ruler, auto-refractor (KR-8100P, TOPCON, Japan), and Mobile Application (Eye Measure, 1.22). Two consecutive measurements were performed. The pupillometer measurement was used as the gold standard measurement for the Bland-Altman analysis, and two analyses were conducted: repeated measures ANOVA and Bland- Altman plots to analyze mean differences (MD) and 95% confidence intervals (CI) calculated as MD±1.96* standard deviation (SD).

Results: The measurement method affected IPD distance (F(3, 117)=15.74, p<0.01). The mobile apps resulted in significantly smaller distance IPD measurements than other methods. The PD ruler method yielded significantly larger distance IPD measurements than the pupillometer. For binocular near IPD, there was a significant difference among the methods (F(2, 78)=15.06, p<0.01). Pairwise comparison revealed that IPD ruler measurement was greater than with the other two methods (pupillometer and mobile application), while no difference was found between the pupillometer and mobile application. For consistency of measurement, correlation of two consecutive measurements was carried out, and it was found to be strongly correlated for all methods (r=0.9; p.<01).

Conclusion: Measurement by different tools showed difference of IPD measurement although induced prism due to discrepancy were within the allowed tolerance of less than 0.33 prism diopter (ISO 16034:2002) for all methods. Therefore, mobile App can be efficiently used for screening purposes for many people where limited services are available. However, caution should be exercised when mobile apps are used, such as in complex and for eyes which are misaligned.