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Yaron Rabinowitz, Yelena Bykhovskaya, Xiaohui Li, Ana Laura Canedo; Optical coherence tomography (OCT) combined with videokeratography to detect ‘early’ keratoconus - a new “pachymetry/asymmetry” index to quantify disease severity. Invest. Ophthalmol. Vis. Sci. 2013;54(15):3223. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To develop parameters using a combination of optical coherence tomography (OCT) and videokeratography to ‘early’ detect keratoconus. Setting: Study was performed at the Cornea Genetic Eye Institute in Beverly Hills, CA.
We studied the following groups: 180 normal eyes, 46 eye with moderate keratoconus, 54 eyes with early keratoconus, 7 eyes with ‘forme fruste’ keratoconus and 16 keratoconus ‘suspects’. We performed videokeratography, wavefront analysis and measured OCT indices to determine which combination was the most sensitive for separating all study groups.
A combination of videokeratography and OCT indices (I-S value and Minimum pachymetry) was statistically the most significant in separating keratoconus groups from normals (P<.001). Using a newly derived index, the Minimum pachymetry divided by the I-S value (PA/I-S index) with a cut off of 400, we could identify 100% of early and ‘forme fruste’ keratoconus as being abnormal with 7 normals misclassified (misclassification rate of 2.7%). By adding keratoconus ‘suspects’ to the analysis and using 1.2 as a cutoff point for the I-S value, we classified 5 ‘suspects’ as normal and 11 normal as abnormal (misclassification rate of 7.8%). The new PA/I-S index, with a cut of point of 400, reduced this misclassification rate to 4.4%.
These results demonstrate that OCT combined with videokeratography is more sensitive for the ‘early’ detection of keratoconus than videokeratography alone. We developed a linear PA/I-S index for quantifying keratoconus phenotype severity which can be used as a quantitative intermediate phenotype in genome wide association studies of keratoconus.
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