Reproducibility of rotating Scheimpflug camera imaging system in patients with keratoconus

Purpose:To determine the reproducibility of indices for diagnosis and follow-up of keratoconus measured with Rotating Scheimpflug Camera imaging system (Pentacam). Methods:Three consecutive scans, taken by the same operator, at a 5 minute interval each, were randomly taken on one eye of 14 patients with keratoconus using Pentacam. The parameters taken into evaluation were: corneal volume (CV), maximal keratometry value (K max), radii of curvature (Rh, Rv) and mean keratometry (Rm) of front (CF) and back (CB) cornea, thinnest location (TL), x (X) and y (Y) position of TL, anterior (ACE) and posterior corneal elevation (PCE) of TL.Reproducibility was assessed by calculating percentage coefficient of variation (%CoV) for all parameters except X and Y for which standard deviation (SD) was considered. The effect of mean value on %CoV was tested by regression analysis and their association with R2. Results:Results are shown in Table 1. %CoVs were <2% in all parameters except ACE and PCE (about 5% each). SD was 0.05 for X and 0.31 for Y. Regression analysis was negative and R2 negligible for all parameters except for RmCF (y= -0,2811x +2,3185, P=0.007, R2=0.47) Conclusions:Pentacam %CoVs in patients with keratoconus were low and independent from mean values (except RmCF). Values outside these ranges should be considered suspect for progression of the disease.