Numerical results of the semi-parametric pharmacokinetic–pharmacodynamic modeling of the effects of morphine or morphine-6-glucuronide (M6G) on pupil diameter, using a sigmoid Emaxmodel. *: Baseline pupil diameter did not differ statistically significant between morphine and M6G (Wilcoxon signed rank test: Z =−1.26, P = 0.208). † Pupil diameter at maximum possible constriction after opioid administration (Emax; see fig. 2, top left corner) was taken from an ongoing study that uses higher doses of morphine and M6G than the present ones, achieving maximum pupil constriction (a plateau). * Pupil diameter at maximum constriction was set to the average of the values marked with †.