Effects of decreasing concentrations of tropicamide on sector pupil dilation

We compared the effects of decreasing concentrations of tropicamide on sector pupil dilation. The concentrations of 0.25, 0.125, 0.03125, and 0.0156% tropicamide were instilled on 10 subjects and the horizontal and vertical pupil diameters measured at 0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, and 90 min after drug instillation. We obtained significant pupil dilation with the 0.25% concentration but with progressively decreasing concentrations we obtained a concomitant decrease in pupil dilation, suggesting that it is the inherent action of the constrictor muscle to respond differently than the dilator muscle (no sector dilation), and this effect is not concentration dependent.