Corneal aberrations measured with the Oculus Pentacam HR: repeatability and reproducibility.

PURPOSE: To evaluate the precision of elevation and wavefront aberration measurements with the Pentacam HR. SETTING: Flinders University, Australia DESIGN:: Instrument evaluation study METHODS:: A randomly selected eye of 100 participants was scanned twice with the Pentacam HR by one observer on the three measurement modes: 25-picture, 50-picture and cornea fine. A second observer performed two scans on the same random eye with the 25-picture mode. Repeatability and reproducibility was assessed using the within subject standard deviation (Sw) statistic from a one-way analysis of variance. RESULTS: The higher order aberration (HOA) root mean square (RMS) repeatability limit (Sw x 1.96 radical2) for both elevation and wavefront, and anterior and posterior measurements was 0.03mum for all three measurement modes. Anterior, posterior and total corneal wavefront Zernike terms were highly precise, with the majority of Zernike terms displaying a repeatability limit of 0.03mum. The least repeatable measurement was the posterior elevation Zernike term Z1 with the 25-picture scan (repeatability limit 1.50mum). The cornea fine measurement mode provided the most precise measurements. Reproducibility limits (second observer) were similar to repeatability limits with the 25 picture scan mode. CONCLUSION: The Pentacam HR provided highly precise aberration outputs. The most precise measurements are achievable with the cornea fine measurement mode and wavefront aberrations. One should be cognisant of posterior elevation aberration precision particularly for lower radial order and higher azimuthal frequency terms. Accounting for tilt and misalignment of aberrations, all RMS and Zernike aberrations were extremely precise (repeatability and reproducibility limit less than 0.000001mum).