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Vishal Jhanji, Bingzhi Yang, Marco Yu, Christopher K. Leung; Comparative Evaluation of Corneal Thickness and Corneal Elevation using Swept Source Optical Coherence Topography, Scanning Slit Topography and Ultrasound Pachymetry. Invest. Ophthalmol. Vis. Sci. 2012;53(14):99.
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© ARVO (1962-2015); The Authors (2016-present)
To compare corneal thickness and elevation measurements in normal and keratoconic eyes using swept-source optical coherence tomography (SS-OCT) and scanning slit topography.
Central corneal thickness (CCT) was measured by SS-OCT (Casia SS-1000, Tomey, Japan), scanning slit topography (Orbscan IIz, Bausch & Lomb, Rochester, New York) and ultrasound (USP) pachymetry in normal and keratoconic eyes. In addition, thinnest corneal thickness (TCT) and corneal elevation were evaluated.
In normal eyes (n=41), mean CCT measured by SS-OCT (546.1±32.5 µm) was significantly thinner compared with scanning slit topography (557.5±30.1 µm) and USP (556.8±34.1 µm) (p=0.001). The span of 95% limits of agreement between SS-OCT and USP (-20.3 to +5.9) was smaller than that between scanning slit topography and USP (-20.5 to +22.0). Likewise, in keratoconic eyes (n=46), mean CCT measured with SS-OCT (476.7±49.0 µm) was thinner than scanning slit topography (481.6±60.6 µm; p=0.081) and USP (488.6±51.4 µm) measurements (p=0.001). The agreement between SS-OCT and USP (-23.9 to +42.3 µm) was better than that between scanning slit topography and USP (-45.2 to +55.1 µm). Both scanning slit topography and SS-OCT demonstrated adequate reliability in measuring CCT and TCT (all ICCs ≥ 0.964), with significantly higher Intraclass Correlation Coefficient observed with SS-OCT (p-values < 0.001, Bootstrap resampling). Repeatability coefficients with scanning slit topography (18.7 µm for CCT and 19.4 µm for TCT) were around 5 times higher than SS-OCT (3.5µm for CCT and 3.7µm for TCT), suggesting the SS-OCT measurements are more consistent. There were significant differences between anterior and posterior corneal elevation measurements between the two instruments in normal as well as keratoconic eyes (p<0.05). In normal eyes, the 95% LoA were between -0.14 and 0.02 mm for anterior BFS and 0.00 and -0.25 mm for posterior BFS. In keratoconic eyes, the 95% LoA were between -0.06 and 0.49 mm and between -0.31 and 0.20 mm for anterior and posterior BFS respectively.
Corneal thickness and elevation measurements were significantly different between SS-OCT and scanning slit topography. With a faster scan-speed, better reproducibility coefficient and higher image resolution, SS-OCT may provide a reliable alternative for measurement of corneal parameters.
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