Posters

Comparison of pachymetry measurements using two optical coherence tomography devices and rotating Scheimpflug imaging in eyes with keratoconus

Poster Details

First Author: Y. Xu NORWAY

Co Author(s): X. Chen   W. Zhou   T. Utheim   A. Stojanovic           

Abstract Details

Purpose:

To compare pachymetry measurements using spectral-domain optical coherence tomography (SD-OCT), swept source OCT (SS-OCT), and rotating Scheimpflug imaging in keratoconic eyes before and after combined treatment by topography-guided transepithelial custom ablation and corneal collagen crosslinking.

Setting:

SynsLaser Kirurgi AS, Tromsø, Norway.

Methods:

Eighty-seven preoperative keratoconic eyes and 55 keratoconic eyes after the combined treatment underwent three consecutive pachymetry measurements with SS-OCT (Casia SS-1000), SD-OCT (RTVue-100), and with Scheimpflug imaging (Precisio). Corneal thickness at the apex and the thinnest point were analyzed. Postoperative eyes were divided into three groups based on the appearance of the demarcation line: 1) absent, 2) patchy and 3) well-delineated. Intra-class correlation coefficients (ICCs) were calculated to evaluate the measurement repeatability, while paired t-test or Wilcoxon signed rank test was applied to evaluate the inter-device agreement. ANOVA was used to compare the measurements between postoperative groups.

Results:

Measurements were highly repeatable with all three devices (ICC>0.94). Preoperatively, corneal thickness values from the three devices were highly correlated (R>0.92). Casia showed slightly thinner values at apex (499.9±36.3μm) and thinnest point (475.6±31.1μm) compared to respective values measured with RTVue (510.1±39.3,485.7±34.9µm) and Precisio (505.6±36.9,485.7±34.9µm). Postoperatively, Precisio demonstrated lower values at apex and thinnest point (456.5±53.0,420.3±56.0µm) than RTVue(490.0±43.0,442.0±37.8µm) and Casia(475.0±40.8,428.0±36.3µm). The measurement differences between Precisio and the two OCTs were larger in postoperative group 3 than in group 1(p<0.05).

Conclusions:

The measurement repeatability was high with all three devices both preoperatively and postoperatively. SS-OCT demonstrated slightly lower values preoperatively, whereas Scheimpflug imaging showed significantly lower values postoperatively. Postoperative corneal transparency might have affected the corneal thickness measurements with Scheimpflug imaging.

Financial Disclosure:

None