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Maolong Tang, Yan Li, Julie Marie Schallhorn, Winston Chamberlain, David Huang; An OCT-based comprehensive classification system of corneal shape irregularities. Invest. Ophthalmol. Vis. Sci. 2017;58(8):3507. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To develop a classification system of corneal shape irregularities based on OCT’s unique ability to map epithelial thickness, pachymetry, and anterior/posterior topography. The system will be tested for detecting forme fruste keratconus (FFK) as well as differentiating FFK from other causes of corneal irregularities.
FFK are better eyes (KISA% < 60) of highly asymmetric keratoconus patients. Other causes of corneal shape irregularities include epithelial basement membrane dystrophy (EBMD), dry eye, contact lens-related warpage, granular dystrophy and eyes after penetrating keratoplasty (PK). Anterior & posterior mean curvature, pachymetry and epithelial thickness maps were obtained from a commercial Fourier-domain OCT system (Avanti). Epithelial Patterns Standard Deviation (Epi-PSD) was calculated to identify irregulars. Four novel OCT-based classification indices were developed and used as input of a 4-level design tree: (1). Epithelium-Anterior Topography (EAT) Index is calculated by the covariance of the epithelial pattern deviation map and the anterior mean curvature pattern deviation maps. (2). Ectasia Index captures coincident posterior steepening and stromal thinning by multiplying the magnitudes of Gaussian fits of the posterior means curvature pattern deviation map and the pachymetry pattern deviation map. (3) Pachymetry-Anterior Topography (PAT) Index is the covariance of the pachymetry pattern deviation map and the anterior mean curvature pattern deviation map. (4) coincident-Thinning (CT) Index captures coincident pachymetric and epithelial thinning by multiplying the magnitudes of Gaussian fits of the pachymetry pattern deviation map and the epithelial pattern deviation map.
The study includes 15 normal eyes, 45 keratoconus, 8 FFK, 3 EBMD, 3 dry eye, 11 warpage, 5 granular dystrophy, and 2 post-PK eyes. Among all 77 abnormal eyes, 74 (96.1%) have abnormally high Epi-PSD. Of the detected abnormal eyes, classification was correct in 100% of 45 keratoconus eyes, 71% of 7 FFK eyes (100% for 3 FFK with no contact lenses and 50% for 4 FFK wearing hard contact lenses), 100% of 9 warpage eyes, 67% of 3 dry eyes, 80% of 5 granular dystrophy and 100% of 2 post-PK eyes.
The OCT-based parameters are useful input for a comprehensive classification of corneal shape irregularities.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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