Figure 1: Testing the influence of the corneal thickness on the progression of corneal PD. Each point in the graph represents values of progression and corneal thickness in one patient. The regression line has a decreasing trend at the correlation coefficient r = -0.2675 (p = 0.0043). It is therefore, a statistically significant indirect dependence of the progression on the corneal thickness. Thus, the thicker the cornea, the smaller is the value of progression. The value of the correlation coefficient r = -0.2675 shows, however, rather weak dependence.