ePoster

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Title:

Confidence intervals for assessing ectatic changes post cross-linking using the ABCD grading system

Poster Details

First Author: H. Jang USA

Co Author(s):    M. Belin   M. Borgstrom   F. Hafezi   E. Flockerzi   B. Seitz        

Abstract Details

Purpose:

The ABCD progression display (Pentacam, Oculus GmbH, Wetzlar, Germany) monitors for ectasia progression and demonstrates statistically significant changes by displaying 80% and 95% one-sided confidence intervals (CI) of each measured parameter. The parameters are anterior (A) and posterior (B) radii of curvature taken from a 3.0 mm optical zone centered on the thinnest point and thinnest pachymetry reading (C). Currently, CI after corneal cross-linking (CXL) is not displayed, as measurement noise post-CXL has not been established. Our study aimed to measure noise of post-CXL eyes with a minimal follow-up of one year and provide CI for this group.

Setting:

Pentacam measurements of post-CXL eyes were taken at ELZA Institute (Zurich, Switzerland) and Homburg Keratoconus Center (Homburg, Germany). Statistical analyses were performed at the University of Arizona, Tucson, USA.

Methods:

Patients from ELZA Institute (Zurich, Switzerland) and Homburg Keratoconus Center (Homburg, Germany) with a minimum of 12 months post-CXL were enrolled. Three separate Pentacam measurements were taken for each eye, removing the patient from the Pentacam device between each measurement. A minimum 7.5 mm of coverage and an acceptable quality score were required. Pooled variance, standard deviations (SD), and one-sided CI were computed. Site specific and time specific comparisons were made using nonparametric statistics.

Results:

60 eyes (38 Zurich, 22 Homburg) of patients aged 29.5 ﾱ 12.3 (range 11-62) were enrolled. Patients were 26.1 ﾱ 19.3 months (range 12-28 Zurich, 16-115 Homburg) post-CXL. The values of ABC parameters and their respective noise measured as SD were all comparable between sites. A subgroup analysis of eyes from Homburg comparing 16-35 months to 38-115 months post-CXL showed no difference in SD. There was no correlation between time post-CXL and SD in all parameters. The 80% CI of ABC parameters were 0.0283, 0.0492, and 3.682, respectively. The 95% CI were 0.0553, 0.0962, and 7.196, respectively.

Conclusions:

Measurement noise of each parameter on the ABCD progression display was analyzed in eyes post-CXL with at least 12-month follow-up period. Noise after 12 months was not correlated with time post-CXL in this group. CI of each measured parameter were computed as above and will be incorporated into the next iteration of the Belin ABCD progression display.

Financial Disclosure:

receives consulting fees, retainer, or contract payments from a company producing, developing or supplying the product or procedure presented