Repeatability of measurements of interpupillary distance.

The purpose of this study was to determine inter- and intra-examiner repeatability of measurements of interpupillary distance (IPD). Three methods were used: Viktorin's, corneal reflection, and pupillometer. In Experiment 1, an experienced optometrist measured IPD on forty-nine subjects, on two occasions, using each method. In Experiment 2, thirty-five optometrists measured the IPD of one subject, on one occasion only, using the same three methods. The results of Experiment 1 showed that measurements of IPD differed depending on the method used, although the differences were small. The 95% limits of agreement were largest with Viktorin's method and least with the pupillometer. The results of Experiment 2 also revealed a small difference in IPD between the three methods of measurement. As in Experiment 1, the 95% limits of agreement were greatest with Viktorin's method and least with the pupillometer. Small differences in IPD were found between Viktorin's, corneal reflection and pupillometer methods of measurement. Not surprisingly, inter-examiner repeatability was slightly poorer than intra-examiner repeatability. However, the differences were small enough not to be clinically significant for the majority of patients.