Comparing Repeatability and Agreement between Commonly Used Corneal Imaging Devices in Keratoconus.

Abstract

Keratometry and pachymetry are important for diagnosis and monitoring of keratoconus. Many corneal imaging units exist but comparison to determine repeatability and agreement are paramount for adequate keratoconus management in primary and secondary care. To evaluate the repeatability and agreement of a Placido disc-based videokeratoscope (Medmont-E300 topographer) used in primary care with spectral-domain optical coherence tomography (Revo-NX) and Scheimpflug corneal tomography (Pentacam-AXL) in secondary-care. This was a prospective, single-center study where one eye was randomized to have central and thinnest corneal thickness (CCT, TCT) and maximum, mean, steep and flat keratometry (Kmax, Kmean, Ksteep and Kflat), measured with all three devices. Three measurements were completed per device to assess intra-observer repeatability. 110 eyes from 110 patients with keratoconus were analyzed. Repeatability was best with the Pentacam for CCT, Kmax, Kmean, Ksteep and Kflat parameters (precision = 9.21,0.8,0.38,0.52,0.58). The Medmont had better repeatability than the Revo with Kmax, Kmean, Ksteep and Kflat (precision = 1.41,1.35,1.43,1.59). Revo had the best repeatability with TCT (precision = 3.81). The intraclass correlation coefficient was ˃0.94 for all parameters in all devices. Agreement was generally poor between devices. However, there was good agreement between Pentacam and Medmont Kflat measurements (P˃.05). Repeatability of keratometry parameters with the Pentacam and Medmont were greater than the Revo, suggesting a lower threshold for change for anterior corneal changes. The Revo had the greatest repeatability for TCT, suggesting a lower threshold for assessing thinning in disease progression and corneal-crosslinking safety. There was poor agreement between devices so devices cannot be used interchangeably.