Table 1.

Summary of Indexes Used to Train the ANN

SIF and SIB—Symmetry index of the anterior and posterior surface	The symmetry index of the SIF is defined as the difference of the mean anterior Gaussian curvature (expressed in diopters) of two circular zones centered in the inferior and superior hemispheres on the axis at 81°/261° or 99°/279° (according to the right or left laterality, respectively). Similarly, the symmetry index of the SIB is defined based on posterior Gaussian curvature.
CSIF and CSIB—Anterior and posterior center-surrounding index	The Center-Surrounding Index of the anterior curvature (CSIF) and the Center-Surrounding Index of the posterior curvature (CSIB) are defined as the difference of the mean Gaussian curvature expressed in diopters—anterior for CSIF and posterior CSIB—of a central circular zone with a radius of 1.5 mm and the concentric annulus with a major radius of 3 mm and a minor radius of 1.5 mm.
EIF—Ectatic index anterior	The EIF could be expressed as a multi-quadratic combination of Zernike coefficients of anterior surface decomposition such to maximize the difference between Normal and Keratoconus subjects as $$\begin{array}{c}\hfill \sum _{k=1}^2\sum _{n,m}{\alpha }_{nmk}{\left(c_n^m\right)}^k\end{array}$$ where $c_n^m$ is the Zernike coefficient with radial order n and azimuthal frequency m, αnmk is its relative weight.
EIB—Ectatic index posterior	The EIB could be expressed as a multi-quadratic combination of Zernike coefficients of posterior surface decomposition such to maximize the difference between normal and keratoconus subjects as $$\begin{array}{c}\hfill \sum _{k=1}^2\sum _{n,m}{\alpha }_{nmk}{\left(c_n^m\right)}^k\end{array}$$ where $c_n^m$ is the Zernike coefficient with radial order n and azimuthal frequency m, αnmk is its relative weight.
RMSF and RMSB—Root mean square of the anterior and posterior surface	RMSF represents the deviation of the anterior elevation from a reference surface, with physiological asphericity Q = −0.2 (average value of healthy normal population) and best-fit apical radius and toricity calculated on an 8 mm diameter circular zone centered on corneal vertex. Similarly RMSB is calculated in reference to an aspho-toric surface, with physiological asphericity Q = −0.3.
ThkMin—Minimum corneal thickness	The minimum corneal thickness is in the central 8 mm diameter zone.
SITHK—Symmetry index of the corneal thickness	The symmetry index of the thickness is defined as the difference of the mean thickness of two circular zones centered in the inferior and superior hemispheres having their center on the axis at 81°/261° or 99°/279° (according to the right or left laterality, respectively).
%TI—Max percentage thickness increase	%TI index is defined as the maximum difference of percentage thickness increase of current pachymetry and the 95th percentile of the normal healthy population.
%EpiTI—Max percentage of epithelial thickness increase	Similar to %TI, %EpiTI index is defined as the maximum difference of Percentage of Epithelial Thickness Increase between of current pachymetry and the 95th percentile of normal healthy population.
KMaxF and KMaxB—Anterior and posterior apical value	KMaxF is defined as the maximum value of the anterior gaussian curvature map. Similarly KMaxB is defined as the maximum value of the posterior gaussian curvature map.
KavgF—Average anterior curvature	If we consider the values of average axial curvatures (in mm) of the two principal meridians of the front corneal surface Rff and Rfs. KavgF is calculated as their average. Both Rff and Rfs are, for their respective meridian, the average values in the central zone within a diameter of 3 mm.
KavgB—Average posterior curvature	If we consider the values of average axial curvatures (in mm) of the two principal meridians of the posterior corneal surface Rbf and Rbs. KavgB is calculated as their average. Both Rbf and Rbs are, for their respective meridian, the average values in the central zone within a diameter of 3 mm.
DZMaxF and DZMaxB—Most elevated value of elevation anterior and posterior map	DZMaxF is defined as the maximum value of the deviation of the anterior elevation from a reference surface with physiological asphericity Q = −0.2 and best-fit apical radius and toricity calculated on an 8 mm diameter circular zone centered on corneal vertex. Similarly DZMaxB is calculated in reference to an aspho-toric surface, with physiological asphericity Q = −0.3.
Spread of the NPS	According to the following points, we can define the NPS as the average distance of the notable points from their barycenter: • $PEpiTh{k}_{Min}$. the location of the minimum of epithelial thickness layer. • $PStrTh{k}_{Min}$. the location of the minimum of stromal thickness layer. • $PTh{k}_{Min}$. the location of the minimum of corneal thickness. • $P{K}_{max}^F$ the location of maximum value in diopters (or the minimum in mm) of the Gaussian curvature for the anterior corneal surface. • $P{K}_{max}^F$ the location of maximum value of the Gaussian curvature for the posterior corneal surface.• $P$ DZMaxF the location of the maximum height derived from the anterior elevation vs. normality map. • $P$ DZMaxB the location of the maximum height derived from the posterior elevation versus normality map.

NPS, notable points radius; SI^B, posterior curvature; SI^F, anterior curvature.