Aqueous vs viscous phenylephrine. II. Mydriatic effects

J. C. Folk, V. Kumar, J. G. Piper, W. A. Barcellos, R. D. Schoenwald and D. S. Chien

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.