Repeatability of pupil size measurements with NIDEK OPD-Scan III in myopic children

Objective: To investigate the repeatability of pupil size measurements, determined from the NIDEK OPD-Scan III, of myopic eyes in children wearing single-vision spectacles (SVS), undergoing orthokeratology (OK) and receiving combined treatment of 0.01% atropine and orthokeratology (AOK). Methods: A single examiner took two sets of mesopic pupil size measurements from the right eyes of 80 children (SVS:16, OK: 34, AOK: 30) (mesopic 1 and mesopic 2) and two sets of photopic (photopic 1 and photopic 2) pupil size measurements (internal light source) using the NIDEK OPD-Scan III. Each set was taken at a single visit, 15 min apart. Subjects in the OK and AOK groups had undergone treatment for at least 6 months, and the SVS subjects had no previous myopia treatment other than wearing spectacles. Repeatability of measurements was analysed using intraclass correlation coefficient (ICC), Bland-Altman (BA) plot, and coefficient of repeatability (CoR). Results: Mesopic 1 and 2 values were not significantly different among the three groups (p = 0.56, 0.77), hence the data were pooled for each set of measurements (mean [±S.D.] values were 7.09 ± 0.61 and 7.12 ± 0.61 mm, respectively) for further analyses. ICC for repeated mesopic pupil size measurements was 0.98 (95% CI, 0.98–0.99). No significant correlation was found between the means of the mesopic 1 and 2 measurements and their differences (Pearson's r = −0.02, p = 0.83). A BA plot also demonstrated narrow 95% limits of agreement, with a CoR of 0.28 mm. Mean photopic 1 and 2 measurements for the AOK group (3.74 ± 0.46; 3.73 ± 0.43 mm, respectively) were significantly larger (p = 0.01; 0.009) than those of the SVS and OK groups, but no significant difference was found between the latter two groups (p > 0.05). Hence, photopic 1 and 2 measurements for the SVS and OK groups were pooled (SVS-OK) for further analyses. ICC for repeatability of the photopic measurements was 0.98 (95% CI, 0.96 to 0.99) for the SVS-OK and AOK groups. The differences between photopic 1 and 2 measurements were not significantly correlated with their means, either in the AOK group (Pearson's r = −0.25, p = 0.19), or in the pooled SVS-OK group (Pearson's r = −0.04, p = 0.78). BA plots also showed narrow 95% limits of agreement, and CoR was 0.25 mm and 0.23 mm in the AOK and pooled SVS-OK groups, respectively. Conclusion: Mesopic and photopic pupil size measurement using the NIDEK OPD-Scan III was highly repeatable and suitable for use on children.