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Study: no effect on ocular circulation seen with Viagra
Nitrate compounds increase optic nerve head circulation; researchers evaluated whether sildenafil would act similarly.
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PHILADELPHIA — Patients treated with Viagra (sildenafil citrate, Pfizer) had no significant change in blood flow to the optic nerve rim or choroid in a study here. There were also no significant changes in intraocular pressure (IOP), ocular perfusion pressure or systemic blood pressure.
“We have previously reported that nitrate compounds, a different group of nitric oxide-mediated vasodilators used mainly for the treatment of ischemic cardiac diseases, produce an increase in optic nerve head and retinal venous vasodilation,” wrote Juan E. Grunwald, MD, and colleagues in the American Journal of Ophthalmology.
“In addition to its vasodilatory properties, sildenafil also has a somewhat lower affinity for phosphotdiesterase type 6, an important component of the phototransduction cascade. This has led to some questions regarding some of the visual effects of sildenafil, such as difficulty in blue-green color discrimination and transient blurry vision.”
Purpose, patients and methods
Fifteen healthy men, aged 30 years and older with visual acuity of 20/25 or better, were included in a randomized, double-masked, placebo-controlled crossover study. Patients had normal eye examinations and an IOP of 21 mm Hg or less. They were assigned either 100 mg of sildenafil or placebo.
“The purpose of this investigation was to evaluate the effect of sildenafil on ocular circulation,” Dr. Grunwald and colleagues said.
To assess optic nerve rim and choroidal circulation, researchers used laser Doppler flowmetry (Oculix Inc.). Patients were asked to focus on a weak laser beam delivered to the eye through a fundus camera. Researchers then measured relative choroidal blood velocity, volume and flow from the center of the foveola as the patients fixated on the laser beam.
IOP was measured, and brachial artery systemic blood pressure was assessed after baseline flow determinations were obtained. Researchers estimated perfusion pressure as two-thirds of the mean blood pressure minus the IOP. Patients were given 100 mg of sildenafil or matching placebo immediately after these measurements were taken. Blood flow and blood pressure measurements were taken at 1 hour and 5 hours after receiving the pill.
Results
Grunwald and colleagues reported that they found no significant change in the mean foveolar choroidal blood flow (P=.88) after sildenafil treatment. Mean foveolar choroidal blood flow was 14.3 ± 3.3 arbitrary units (±SD) at baseline, 13.4 ± 3.1 arbitrary units at 1 hour and 13.1 ± 2.7 arbitrary units at 5 hours. After treatment with placebo, the baseline reading was 14.1 ± 3.6 arbitrary units, 13.1 ± 3.6 arbitrary units at 1 hour and 13.2 ± 3.4 arbitrary units at 5 hours.
Researchers also found no significant change in mean optic nerve blood flow (P=.53) in patients assigned sildenafil. Mean optic nerve head blood flow was 11.6 ± 2.2 arbitrary units at baseline, 12.5 ± 2.8 arbitrary units at 1 hour and 12.1 ± 2.4 arbitrary units at 5 hours. After treatment with placebo, the baseline reading was 11.9 ± 2.5 arbitrary units, 12.6 ± 3.1 arbitrary units at 1 hour and 13 ± 3.0 arbitrary units at 5 hours, investigators wrote.
When compared with the placebo group, patients in the sildenafil-assigned group had no significant change in IOP (P=.94), mean blood pressure (P=.38) or perfusion pressure (P=.36), according to researchers.
In the sildenafil-assigned group, the mean IOP was 15.2 ± 3 mm Hg at baseline, 16.0 ± 2.9 mm Hg at 1 hour and 15.1 ± 2.8 mm Hg at 5 hours. In the placebo-assigned group, mean IOP was 15.8 ± 2.5 mm Hg at baseline, 15.7 ± 1.9 mm Hg at 1 hour and 14.7 ± 2.3 mm Hg at 5 hours.
“The power to detect a 10% change in [IOP] after sildenafil was approximately 90% (P=.05),” said researchers. “These data also suggest that sildenafil does not significantly affect [IOP] at the maximum clinical dose.”
Mean blood pressure in the sildenafil group was 94 ± 14 mm Hg at baseline, 90 ± 14 mm Hg at 1 hour and 92 ± 11 mm Hg at 5 hours. In the placebo group, mean blood pressure was 97 ± 10 mm Hg at baseline, 96 ± 14 mm Hg at 1 hour and 94 ± 11 mm Hg at 5 hours.
Mean perfusion pressure in the sildenafil group was 47 ± 9 mm Hg at baseline, 44 ± 9 mm Hg at 1 hour and 46 ± 7 mm Hg at 5 hours. In the placebo group, mean perfusion pressure was 49 ± 7 mm Hg at baseline, 49 ± 10 mm Hg at 1 hour; and 48 ± 7 mm Hg at 5 hours.
“We have been interested in the effects of nitrates on the circulation of the eye because of their potential therapeutic effects on ocular vascular diseases, one of the main causes of visual impairment. Compounds that can achieve vascular dilation and increased blood flow would greatly facilitate the treatment of these types of diseases. In this group … sildenafil did not cause any significant change in [IOP],” said Dr. Grunwald and colleagues.
Researchers said they believe this information could be important to glaucoma patients who are receiving sildenafil therapy. They noted, however, that more data on the effect of sildenafil on the IOP of patients with glaucoma are needed to make any strong conclusions regarding this issue.
For Your Information:
- Juan E. Grunwald, MD, can be reached at the Scheie Eye Institute, Department of Ophthalmology, University of Pennsylvania, 51 N. 39th St., Philadelphia, PA 19104; (215) 662-8039; fax: (215) 662-0133; e-mail: juangrun@mail.med.upenn.edu. Dr. Grunwald has no direct financial interest in the products mentioned in this article, nor is he a paid consultant for any companies mentioned.
Reference:
- Grunwald JE, Siu KK, et al. Effect of sildenafil citrate (Viagra) on the ocular circulation. Am J Ophthalmol. 2001;131:751-755.