PURPOSE. To determine whether two corneal reflection pupillometers, the new Grobet PD Meter and the industry-standard Essilor PRC, provide similar measures of the anatomical interpupillary distance, or PD. METHOD. The distance and near PDs of 85 subjects were measured with the Grobet PD Meter and the Essilor PRC by two experienced examiners. The data were analyzed using the standard method of determining agreement between methods of clinical assessment and with a repeated-measures general linear model.
RESULTS. There was no agreement between the PDs measured with these devices. The distance and near PD measurements averaged between 1.1 and 1.7mm larger with the Grobet PD meter than with the Essilor PRC. These differences were significant (t values from 9.3 to 22.4, p =0.000). The repeated measures analysis also revealed that the devices provided different PD measures (F = 661.1, p =0.000). Finally, there was also a difference in the PD measurements between the examiners (F = 48.3, p = 0.000).
CONCLUSIONS. The difference in PD measures between the two devices could create a clinical dilemma, especially when fitting progressive addition lenses, or PALs. The performance of these lenses are highly dependent upon accurate horizontal positioning before the eyes. While it is recognized that other factors influence patient satisfaction with PALs, chief amongst them, vertical positioning, choice of lens, and frame suitability, it is clear that an improper PD can contribute to their ultimate acceptance or rejection. The inter-examiner difference might be the result of the fact that the Grobet PD Meter does not have a forehead bar that permits more precise positioning on a patient’s face or it may result from other design differences between the devices. Further testing may determine how significant the clinical difference in measurements between these instruments truly are.