PURPOSE. Two classes of drugs, sympthomimetics (phenylephrine [P]) & parasympatholytics (tropicamide [T], cyclopentolate [C]) are used for dilation during eye examinations. Agents are frequently combined in an attempt to improve dilation & shorten time course. However, it is unclear if one combination provides a greater or faster dilation than the other. Time course & magnitude of dilation achieved with TP (1% T, 2.5% P) & TC (1% each) were compared in patients with dark irides. METHOD. 45 subjects, 4 to 32 yrs of age, with dark irides (grades 4 or 5; Seddon, et al 1990) were enrolled. Photographs were taken prior to dilation & at 5, 10, 15, 20, 40, & 60 minutes after instillation of each drug combination. Subjects received TP in one eye & TC in the fellow eye. Eyes were randomized for combination received. An examiner masked to drug combination & time used a digital analysis program to analyze photos. 5 estimates of each pupil area were made, pupil diameter calculated & diameters averaged.
RESULTS. TP produced significantly larger pupils than TC (7.3 mm vs 7 mm; p < 0.0001 paired t-test) & time to maximum dilation was longer with TP than TC (48.6 min vs 45.2 min; Wilcoxon signed rank test p=0.018). However, these small differences were not clinically significant. 98% of pupils reached 6 mm with either TP or TC, & 80% reached 7 mm with TP but only 58% with TC (p=0.0062 McNemars Exact Test for 7 mm comparison). Time at which 50% of pupils reached 6 mm (Kaplan-Meier non-parametric survival analysis) was not significantly different with the 2 combinations (TP 11.56 min TC 12.75 min). However, time at which 50% reached 7 mm was statistically & clinically significant (TP 32.1 min TC 52 min, p=0.0325). When subjects less than or equal to 10 yrs were compared to those older than 10 yrs, there was no significant difference in time at which 50% reached either a 6 mm or 7 mm pupil with TP or TC. However, in every case the younger group took longer.
CONCLUSIONS. A 6 mm pupil dilation (considered adequate for clinical examination) may be obtained with either TP or TC with maximum dilation in 45 to 49 minutes in patients with dark irides. However, more subjects achieved a 7 mm pupil with TP than TC.