BACKGROUND--Patients who have their pupils dilated for an eye examination traditionally have to wait several hours before their pupils return to normal size and their blurred vision (caused by paralysis of accommodation) resolves. Earlier studies with dapiprazole have demonstrated an accelerated reversal of dilatation. METHODS--Three regimens of dapiprazole were studied to determine the effects on pupil diameter and accommodation after mydriasis produced by 2.5% phenylephrine and 0.5% tropicamide. Test regimens included one drop and 1 + 1 drop regimens, compared with a 2 + 2 drop reference regimen. Dapiprazole was administered in one eye and placebo in the other. Mean change from baseline was analysed for pupil diameter and accommodation at various time points after drug administration. Also, for the same variables, 90% confidence intervals for the areas under the curve (AUC) were computed. RESULTS--Both test regimens were equivalent to the reference regimen on the basis of mean change from baseline for pupil diameter and accommodation at individual time points, and for the mean AUC. Most signs and symptoms (injection, stinging, burning, lid oedema, and ptosis) were less frequent in the test regimen treated eyes. There was no significant interaction between regimen and eye colour. CONCLUSION--This study indicates that a lower dosage (for example, one drop) is also efficacious and has the added benefit of fewer side effects.