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Neema Nayeb-Hashemi, John Jesse; Towards a New Keratoconus Screening Paradigm: Correlating Known Risk Factors with the Corneal Spatial Thickness Profile and Biomechanical Properties Obtained from the Ocular Response Analyzer.. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):1132.
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© ARVO (1962-2015); The Authors (2016-present)
Keratoconus (KCN) is a problem that affects millions of individuals worldwide. To this point, there has been no clear way of determining who is at risk of developing KCN until the changes in the cornea begin to manifest in the corneal topographic imaging. We performed a retrospective chart review looking at normal eyes versus eyes with KCN and compared corneal spatial thickness profiles (STP), and Ocular Response Analyzer (ORA) data to determine if there was any correlation which may help predict who is at increased risk of KCN in the future.
Pentacam data and ORA data collected from 100 normal and 32 KCN eyes was reviewed. Using the STP, a third order polynomial best fit was computed using Microsoft Excel. The coefficients of the best fit curve as well as the ORA` data were then analyzed using a multivariable and correlational analysis looking for differences between groups.
In comparing normal eyes to eyes with KCN, STP best fit coefficients were found to be as follows: the constant was 133.5 points lower for KCN vs normal eyes (p<0.001). Conversely, the first, second, and third order coefficient was 20.2, 10.3, and 2.53 points greater for the KCN group (p<0.003). Adjusting for corneal steepness however, the third order coefficient was found to be insignificant (p>0.07). Using ORA data, it was found that the corneal resistance factor (CRF) and corneal hysteresis factor (CHF) was 3.2 and 2.2 points lower for the KCN group respectively (p <0.001). Adjusting for corneal steepness, the differences remained significant. Correlational analysis determined that only the constant was significantly correlated with CRF in both KCN and normal eyes.
While initial studies comparing STP between KCN and normal eyes validated its diagnostic value, little effort has been spent attempting to quantify the differences in order to determine whether a screening protocol can be derived from the coefficients of the best fit. The fact that all the coefficients and the constant were significantly different may be secondary to the severity of KCN in a significant portion of the cohort. Future comparisons of early KCN eyes to normal eyes with similar corneal thicknesses and curvature, will help elucidate whether the coefficients of the STP can be useful in predicting individuals at risk for KCN.
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