I-S value = -0.4575 + 89.5389 (IHD) - 111.8720 [(IHD).sup.2] x ([r.sup.2] = 0.7857, residual SD = 1.1925).
By applying the formula with the inferior half steeper than superior, (I-S) value of 0.5, 1, and 1.4 correspond to IHD of 0.010, 0.014, and 0.017, taking into consideration that IHD values >0.014 are considered abnormal and IHD values >0.016 are considered pathological  (Table 2).
Regarding the validation sample, the IHD, (I-S) value, and the deduced IHD from the abovementioned formula are represented in Table 3.
The AUROC of IHD and (I-S) value were not statistically significantly different from each other (Table 4).
One of these criteria is the curvature asymmetric decentration (I-S) value with a positive value indicating steeper curvature of the inferior half of the cornea.
Our study revealed a high correlation between the (I-S) value and the IHD.
As the Pentacam software does not include the (I-S) value, and there is a high correlation between the (I-S) value and IHD, we deduced regression formulae between them to be able to calculate one from the other with reasonable accuracy.
Caption: Figure 1: (I-S) value calculated astride the horizontal meridian.
Caption: Figure 2: The regression formula deducing the IHD from the (I-S) value with the 95% prediction lines.