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Motozumi Itoi, Hiroe Fukazawa, Eiko Ueda, Masaru Hisae, Kennichi Hayashi; Evaluation of a New Keratoconus Screening System for an Anterior Chamber OCT. Invest. Ophthalmol. Vis. Sci. 2012;53(14):96.
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The anterior chamber OCT (CASIA: SS-1000; Tomey, Inc.) measures, not only anterior corneal surface topography, but also precisely measures the posterior surface and corneal thickness across a wide area. Previous corneal topography-based keratoconus screening systems based their analyses on anterior corneal surface topography. However, it is known that keratoconus causes changes, not only to the anterior surface, but to corneal thickness and the posterior surface as well. Our purpose was to see if an anterior chamber OCT keratoconus screening system can provide a more sensitive and specific way to characterize changes in keratoconus relative to previous anterior surface methods.
Using the CASIA OCT, we compared basic corneal parameters for 232 moderate to advanced keratoconic eyes (116 subjects) and 180 normal eyes (90 subjects).
All parameters measured in this study (anterior BFS, posterior BFS, anterior elevation, posterior elevation, anterior steepest instantaneous radius, posterior steepest instantaneous radius, anterior asymmetry (6 mm, Fourier), posterior asymmetry (6 mm, Fourier), minimal thickness, center thickness, mean peripheral thickness (3 mm from the center)) showed significant differences between keratoconic and normal corneas. The smallest p value was found for posterior steepest instantaneous radius; next was posterior asymmetry. All posterior surface parameters showed smaller p values than anterior surface parameters. Histogram analysis showed best discrimination for posterior asymmetry; next best was posterior steepest instantaneous radius.
The most marked topographic changes in keratoconic eyes were in the posterior surface rather than the anterior surface or corneal thickness. In particular, the most conspicuous differences between normal and keratoconic eyes were seen for posterior asymmetry and posterior steepest instantenous radius. Using the posterior surface parameters of anterior chamber OCT, we may create more sensitive and specific keratoconus screening system.
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