Repeatability of the Pentacam HR in various grades of keratoconus.

Abstract Purpose To evaluate the repeatability of an extensive number of relevant indices with the Pentacam HR in keratoconus of varying severity and normal eyes. Design Reliability analysis Methods This study was performed at Antwerp University Hospital, Belgium, and enrolled 20 healthy volunteers (20 eyes) and 69 patients (69 eyes) with keratoconus. Three consecutive measurements were performed by the same operator with Pentacam HR in keratoconus and normal eyes. Exclusion criteria included: past ocular surgery, recent rigid contact lens wear and corneal scarring. The keratoconus group was subdivided according to the Belin/Ambrosio total deviation value (BAD-D): subclinical, mild and moderate. The within-subject standard deviation (Sw) and repeatability limit (r) were computed for repeatability assessment. The tolerance index (TI) was calculated to compare across parameters with different measurement scales. For the sample size included, TI > 0.36 signified statistical significance at the 0.05 level. Results Repeatability in subclinical keratoconus did not differ significantly from controls (p>0.05), except for wavefront aberrations. In mild keratoconus, 11/18 (61.1%) anterior corneal, 7/14 (50%) posterior corneal, 2/5 (40%) pachymetry, 7/11 (63.6%) combined and 1/6 (16.7%) densitometry parameters showed significantly worse repeatability compared to controls (TI>0.36). Repeatability of most parameters worsened in moderate disease. In particular, Kmax and anterior astigmatism showed significantly worse repeatability in moderate keratoconus. Conclusions Measurement variability of Pentacam HR is of clinical relevance when assessing for progression of keratoconus. We provide reference repeatability values and scale independent analysis of relevant corneal parameters in keratoconus of varying degree.