Comparison of two drug combinations for dilating dark irides

Two combinations of dilation drops [1% tropicamide and 2.5% phenylephrine (TP) vs. 1% tropicamide and 1% cyclopentolate (TC)] were compared to determine time course and magnitude of dilation for patients with dark irides.

Forty-five subjects, aged 4 to 32 years, with dark irides were enrolled. Photographs were taken before dilation and at 5, 10, 15, 20, 40, and 60 min after instillation of drops. Subjects received TP in one eye and TC in the fellow eye, with eyes randomized to the combination received. An examiner masked to drug combination and time used digital analysis to calculate pupil diameter for each photograph. TP and TC were compared to determine the time to reach both 6- and 7-mm pupil diameter and the percentage of subjects reaching these diameters.

Ninety-eight percent of pupils reached 6 mm with either combination; however, 80% reached 7 mm with TP and only 58% with TC (p = 0.0062, McNemars exact test). Time at which 50% of pupils reached 6 mm was not significantly different between drug combinations (TP 11 min vs. TC 12 min, Kaplan-Meier survival analysis). However, time at which 50% reached 7 mm was statistically and clinically significant (TP 32 min vs. TC 52 min, p = 0.0325). For subjects < or =10 years vs. >10 years, there was no significant difference in time at which 50% reached a 6- or 7-mm pupil with TP or TC; however, in every case, the younger group took longer.

A 6-mm pupil dilation may be obtained with either TP or TC; however, more subjects achieved a 7-mm pupil with TP than TC and had a faster time course to attain that size.