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Ibopamine More Potent Mydriatic Than Phenylephrine Or Tropicamide

Ibopamine alone has a more potent mydriatic effect and increase in intraocular pressure in patients with glaucoma than do either phenylephrine or tropicamide.

Researchers from the University of Verona, Italy, enrolled 15 patients with primary open-angle glaucoma and 15 healthy subjects, aged between 40 and 70 years (mean 54.8), into this open prospective study. Assessments were mad of visual acuity, refraction, intraocular pressure (IOP), pupil diameter and anterior segment geometry after instillation of 2% ibopamine. Between 20 and 30 days later, five controls and five glaucoma patients underwent the same assessments using first 10% phenylephrine followed by 1% tropicamide.

Another group of 15 healthy controls, aged between 45 and 70 years (mean 53.5) was recruited. In this group, the researchers measured pupil diameter following various doses of ibopamine, phenylephrine and tropicamide.

Forty minutes after treatment with 2% ibopamine, average pupil size increased from 5.0 to 9.1 mm. This mydriasis was greater than either 10% phenylephrine (4.7 to 7.9 mm) or 1% tropicamide (4.6 to 6.9 mm). Ibopamine did not alter either refraction or visual acuity.

In glaucoma patients, IOP rose from 22.2 to 24.8 mm Hg following ibopamine. After instillation of 1% tropicamide, IOP increased from 21.2 to 23.6 mm. However, 10% phenylephrine did not produce any statistically significant change in IOP.

Ibopamine 2% increased iris thickness, while reducing the depth of the sulcus ciliaris and posterior chamber. The anterior chamber angle widened by a mean of 5 degrees. The scleral-iris and sclera-ciliary process angles both increased. The pupil border and lens surface separated in 37% of cases. In the remainder, contact with the zonule only remained.

Phenylephrine 10% produced a similar pattern of changes. However, only the increase in iris thickness and scleral-iris angle reached statistical significance. Tropicamide slightly increased the scleral-iris angle, which was also statistically significant.

The authors concluded that 2% ibopamine is a more potent mydriatic than either 10% phenylephrine or 1% tropicamide. Ibopamine also increases IOP in glaucoma patients. The findings suggest that ibopamine widens the anterior chamber angle by posterior rotation of the iris plane and ciliary processes. Ibopamine's more marked effect compared to phenylephrine and tropicamide seems to underlie the greater mydriasis.
Invest Ophthalmol Vis Sci 2003;44:281-9. "Comparative study of the effects of 2% ibopamine, 10% phenylephrine, and 1% tropicamide on the anterior segment."

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