OPD-Scan III: a repeatability and inter-device agreement study of a multifunctional device in emmetropia, ametropia, and keratoconus.

The purpose of this study was to test the measurements of a multifunctional device, the NIDEK OPD-Scan III in terms of repeatability and agreement with retinoscopy and Pentacam in cases with emmetropia, ametropia, and KCN (grade 1-3). We enrolled 170 eyes (40 in each group of emmetropia and ametropia, and 90 in the 3 KCN subgroups). Acquisitions were done twice by a single technician to check the intra class correlation, repeatability index, and precision. To assess agreement, we compared OPD-Scan III with retinoscopy and Pentacam results by two blinded technicians. All device functions had acceptable precision in groups with emmetropia, ametropia, and KCN1, except spherical error in ammetropics (0.97 D). In KCN2, repeatability was acceptable with the refractive function, topography, and ocular aberrations but was more than 1.0 D for corneal aberrations. In KCN3, repeatability was low for the refractive function and corneal spherical aberration. Refractive data were not convertible to those obtained by retinoscopy in any group. OPD-Scan III keratometry data were interchangeable with Pentacam counterparts in emmetropes, ammetropes, and KCN1. In KCN2, the OPD-Scan III-Pentacam agreement for Kmax was 0.71 D, and there was 1.25 D difference in Kmin. No OPD-Scan III-Pentacam agreement was observed in KCN3. OPD- Scan III is a multifunctional device with acceptable repeatability in emmetropic, ammetropic, and KCN cases. Its measurements of corneal curvature and ocular aberrations are better than other functions. In cases with high degrees of refractive error and corneal irregularities, device repeatability and agreement with Pentacam is decreased.