New Oct Classification For Keratoconus Severity

The seminal but still widely used KC severity classification is the Amsler-Krumeich’s Severity Classification (AKSC). Topographers have improved a lot since then and, these evolutions need to be now correlated to an updated classification. We have worked on elaborating and testing a new severity classification with the help of the OCT based corneal topography technology, called Touboul / Bordeaux’s Severity Classification (BSC).

Bordeaux University and hospital, National Reference Center for Keratoconus (CRNK)

A descriptive prospective monocentric study was held in the CRNK of Bordeaux (France) in 2021, involving 282 consecutive keratoconic eyes. The AKSC and BSC were compared to the Fourier anterior 6 mm asymmetry index (FAAI) chosen as a dependent and comprehensive severity criteria for KC deformation, using linear mixed regression models.

The association of BSC and AKSC with the FAAI severity criteria were both significant (p<0.001) with a linear relationship. In the mixed regression model, AKSC’s stage explained 22% of variance of the FAAI severity criteria (R2=0.22, 95%CI 0.14 to 0.29), the BSC explained 48% of variance of the FAAI severity criteria (R2=0.48, 95%CI 0.40 to 0.55).

We proposed in that study a new topographical severity classification, based on the anatomical changes occurring in the KC course and routinely measurable with the help of OCT technology. Thus, anterior asymmetrical index, corneal thinnest point and maximal keratometry to the apex were used to divide the KC in five intervals of severity level who obtained a better linearity and correlation to corneal asymmetrical factors than the seminal AKSC.