Aqueous vs viscous phenylephrine. II. Mydriatic effects.

We performed four studies to determine whether there is a difference in the mydriatic effect of 2.5% aqueous vs 2.5% viscous phenylephrine hydrochloride solutions. The first study was performed under "room light" conditions, and the mean (+/- SD) dilation at one hour was 0.87 +/- 1.18 mm for the aqueous and 0.86 +/- 1.14 mm for the viscous solutions. The second study was performed in a darkened room, and the mean dilation at one hour was slightly greater than in room light but was still minimal (aqueous, 1.14 +/- 1.00 mm; viscous, 1.07 +/- 1.11 mm). In the third study, patients were pretreated with a topical anesthetic (0.5% proparacaine hydrochloride), and the mean one-hour dilation was approximately twice (aqueous, 2.30 +/- 0.81 mm; viscous, 2.41 +/- 0.88 mm) that found in patients who were not pretreated with proparacaine. In the fourth study, the two phenylephrine solutions were used in combination with 1% tropicamide, and the mean one-hour dilation was 3.8 +/- 0.82 mm for the aqueous and 3.8 +/- 0.98 mm for the viscous solutions. Our studies show that there is no difference in the mydriatic effect of 2.5% aqueous vs 2.5% viscous phenylephrine solutions when used alone or in combination with 0.5% proparacaine or 1% tropicamide.