Comparative study of the effects of 2% ibopamine, 10% phenylephrine, and 1% tropicamide on the anterior segment

To assess in normal and glaucomatous eyes the effect of the dopaminergic drug 2% ibopamine on visual acuity, IOP, pupil size and anterior segment geometry, compared with 10% phenylephrine and 1% tropicamide.

Fifteen healthy subjects and 15 patients with primary open-angle glaucoma, aged from 40 to 70 years (mean age: 54.8 +/- 9.6), were recruited into this open prospective study. After instillation of 2% ibopamine, refraction, visual acuity, pupil diameter, IOP, five A-scan ultrasonographic parameters, and 15 ultrasound biomicroscopy parameters were evaluated. The study was repeated with assessment of the same parameters 20 to 30 days later in 10 subjects (5 normal and 5 with glaucoma), using first 10% phenylephrine and then 1% tropicamide. A second group of 15 healthy subjects, aged from 45 to 70 years (mean age: 53.5 +/- 8.6) was examined to evaluate the dose-response effect and time course on pupil diameter, of ibopamine, phenylephrine, and tropicamide.

After 40 minutes 2% ibopamine induced a marked mydriatic effect (from 5 to 9.1 mm; P < 0.0001) greater than that produced by 10% phenylephrine (from 4.7 to 7.9 mm; P < 0.0001) or 1% tropicamide (from 4.6 to 6.9 mm; P < 0.0001), with no changes in refraction or visual acuity. IOP was significantly increased only in patients with glaucoma after instillation of either 2% ibopamine (from 22.2 to 24.8 mm Hg; P < 0.0001) or 1% tropicamide (from 21.2 to 23.6 mm Hg; P = 0.004), whereas 10% phenylephrine induced no statistically significant changes. Ibopamine (2%) caused a significant increase in iris thickness with a reduction of the sulcus ciliaris and posterior chamber depth. The anterior chamber angle (ACA) showed a mean 5 degrees widening with an increase in scleral-iris angle (SIA) and sclera-ciliary process angle. In 11 (37%) of 30 cases, separation of the pupil border and lens surface occurred, whereas contact was maintained only with the zonule in the other 19 (63%) of 30. The changes after 10% phenylephrine instillation were similar, although only the increase in iris thickness and SIA was statistically significant. Tropicamide (1%) induced a slight but significant increase in SIA.

The results confirm the potent mydriatic effect of 2% ibopamine, which is greater than that of either 10% phenylephrine or 1% tropicamide, as well as its ability to induce an increase in intraocular pressure when used in patients with glaucoma alone. These data support the hypothesis that the widening of the ACA induced by 2% ibopamine is due to posterior rotation of the iris plane and ciliary processes. These changes are quantitatively greater than those induced by 10% phenylephrine and 1% tropicamide and are related to the greater mydriatic effect of the drug.