Effect of keratoconus grades on repeatability of keratometry readings: Comparison of 5 devices

To determine the repeatability of keratometry (K) measurements of a Scheimpflug pachymeter (Pentacam), Placido topographer (Eyesys), scanning-slit corneal topographer (Orbscan), partial coherence interferometry (PCI) device (IOLMaster), and Javal manual keratometer with different grades of keratoconus.

Noor Eye Hospital, Tehran, Iran.

Retrospective case series.

Keratometry was performed first with Scheimpflug pachymetry followed, in order, by Placido topography, scanning-slit corneal topography, PCI, and manual keratometry. Repeatability was examined in groups with a maximum K of less than 50.0 diopters (D), 50.0 to 55.0 D, and more than 55.0 D.

Seventy-eight eyes of 45 keratoconus patients were assessed. In Group 1, repeatability was highest with Scheimpflug pachymetry and lowest with scanning-slit corneal topography (0.36 to 1.24). In Group 2, the intraclass correlation coefficients (ICCs) for maximum K ranged from 0.823 with the scanning-slit corneal topography to 0.974 with Scheimpflug pachymetry. The repeatability index for minimum K (0.53 to 2.11) and maximum K (0.60 to 1.92) in this group was highest with Scheimpflug pachymetry and with for scanning-slit corneal topography. In Group 3, the ICCs for minimum K and maximum K ranged from 0.890 to 0.990, and the repeatability index for minimum K varied between 1.66 with Scheimpflug pachymetry to 2.98 with Placido topography; for maximum K, the index was from 2.15 with PCI to 2.81 with the manual keratometer.

In mild keratoconus, the 5 devices had acceptable repeatability in K readings. In cases with a maximum K reading greater than 55.0 D, all devices had reduced repeatability as a result of measurement errors; thus, measurements might not be so reliable.