To test measurements of NIDEK OPD-Scan III in terms of repeatability and agreement with retinoscopy and Pentacam.

We enrolled 120 eyes (40 in each group of emmetropia, ammetropia, and keratoconus) with a mean spherical equivalent of -0.08±0.26 diopter (D), 1.05±0.81D, and -2.90±2.37D, respectively. Acquisitions with OPD-Scan III were done twice to check repeatability,and compared with retinoscopy and Pentacam results for agreement.

In all groups, RI was best for mean keratometry (Kmean) (range, 0.05-0.11). Worst repeatability index (RI) pertained to spherical error in emmetropia (0.34) and ammetropia (0.69), and to corneal higher order aberrations in keratoconus (1.03). The width of agreement (WOA) with retinoscopy was more than 0.50D in all groups; lower amounts of refractive error showed better agreement. In emmetropia and ammetropia, WOA with Pentacam Kmean (0.63D and 0.12D) and asphericity (0.59 and 0.13) were acceptable; these WOA were respectively 2.47D and 8.16 in keratoconus.

In all three groups, OPD-Scan III measurements were acceptably repeatable. Its refractive function showed less repeatability and agreement with retinoscopy at higher levels of refractive error. Measurements of corneal curvature and shape had good agreement with Pentacam in ammetropia and emmetropia. Further studies in post-refractive surgery and keratoconus cases are warranted.