The mydriatic effect of multiple doses of tropicamide

We investigated whether two drops of 0.5% tropicamide produced a wider pupillary dilation when compared with a single drop and saline control in subjects with dark-colored irides.

Twelve young adult subjects with dark irides and who were free from ocular disease participated in the study. One eye of each subject, selected at random, was designated as experimental and the fellow eye as control. A single drop of 0.5% tropicamide was instilled in the lower cul-de-sac of each eye in turn. Immediately after, a second drop of 0.5% tropicamide was instilled in the experimental eye and a single drop of unpreserved saline into the control eye. A double-masked experimental protocol was followed. Digital images of both pupils of each subject were taken at baseline (predrug instillation) and then every 5 minutes up to 30 minutes postdrug instillation and at 40, 50, and 60 minutes. The images were subsequently viewed on a PC monitor, and pupil size was measured using a calibrated millimeter scale.

Pupil diameter increased as a function of time for both conditions reaching a maximum between 20 and 30 minutes after drop instillation. Pupil diameter was greater under the experimental condition compared with the control (analysis of variance p < 0.001). Pupil diameter reached at least 6 mm under both the experimental and control conditions.

In young healthy subjects, compared with a single drop of tropicamide, two drops were associated with a greater degree of pupillary dilation on average over the 60-minute study period. However, the magnitude of the difference was small and not clinically significant. A single drop of tropicamide produced a pupillary diameter of at least 6 mm, which should be sufficient for the conduct of a thorough dilated fundus examination.