FDA has received 43 reports of varying degrees of vision loss, including blindness, in men taking type 5 phosphodiesterase (PDE-5) inhibitors. Most of these cases of vision loss were due to nonarteritic anterior ischemic optic neuropathy (NAION). The loss of vision in some cases has been irreversible.

As type 5 phosphodiesterase (PDE-5) inhibitors are the main active ingredients in Viagra, Cialis and Levitra, the US Food and Drug Administration (FDA) has issued a news release to advise healthcare providers of the potential risk.

NAION is a vascular event that is presumed to occur due to a decrease in blood flow to the small arteries that supply the optic nerve. A disruption in the blood supply to the optic nerve causes damage to the nerve. Injury to the nerve may result in permanent visual loss in 1 or both eyes. Patients are typically older than 50 years of age; clinical examination reveals unilateral visual acuity and visual field loss and optic disk edema. Despite the frequency with which this condition occurs, its exact cause is not known. Numerous risk factors have been proposed, including a small cup-to-disk ratio, hypertension, diabetes mellitus, arteriosclerosis, hypercholesterolemia, and after intraocular surgery.

As patients with erectile dysfunctions are more likely to have the microvascular risk factors typically associated with spontaneous NAION, an ischemic effect by type 5 phosphodiesterase (PDE-5) inhibitors,on the optic nerve is plausible, but unlikely. In normal adults, PDE-5 inhibitors increased pulsatile ocular blood flow, a result of filling the choroidal circulation.

Despite the differences in the number of cases of NAION among men taking the various PDE-5 inhibitors - 38 cases in men using Viagra, 4 in men using Cialis, and 1 case in a man using Levitra - there is no evidence that one drug presents a higher risk than another. Viagra has been used by more than 23 million men worldwide, Cialis by more than 4.5 million, and Levitra by more than 1.8 million. The difference in the number of NAION cases among all 3 PDE-5 inhibitors reflects the number of each drug used worldwide rather than real differences in risk among drugs.

It can be recommended that patients with a history of monocular NAION be cautioned that PDE-5 inhibitors may increase the risk of NAION in the fellow eye. At the same time, patients who have risk factors for the development of NAION should be referred to an ophthalmologist before being prescribed PDE-5 inhibitors.