PIP Protein levels measured by western blot analysis from three biological fluids: A: tears, B: Plasma and C: Saliva in patients with KC (n = 147) compared to healthy controls (n = 60). Four KC severity stages were classified according to Kmax values (KC1, KC2, KC3, and KC4). Estimates represent mean and error bars represent standard error of the mean. Mann-Whitney U test was used to test group difference, ***p < 0.001, ****p < 0.0001.