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VIAGRA PROS AND CONS
November 2000

Sildenafil citrate, better known as Viagra (Pfizer), is a relatively new compound that was approved by the Food and Drug Administration (FDA) in the spring of 1998 to treat erectile dysfunction. Shortly thereafter, however, the short-term adverse effects for patients with heart disease were being reported. Within six months about 130 people in the United States died from heart attacks associated with use of the drug. Because of its relatively short time on the market, the scope of its side effects, both good and bad, remains incompletely known.

At about the same time that the potential cardiac implications of sildenafil use were becoming apparent, there were hints that sildenafil was affecting patients in other ways. The American Academy of Ophthalmology (AAO) issued a warning to ophthalmologists dated May 28, 1998. In this press release Michael Marmor, MD, professor of ophthalmology at Stanford University and a spokesperson stated that "a moderate percentage of people (3%) taking twice the recommended dose of Viagra have experienced problems with their vision. Federal Drug Administration clinical trials show that taking the medication, especially at higher doses, can affect the way we see for a number of hours."

Patients reported that their vision had a blue tinge and that they were sensitive to light. In line with this, the Federal Aviation Administration recommended that pilots refrain from taking sildenafil within 6 hours of flying, because individuals "taking higher-than-recommended doses had trouble telling the difference between blue and green," the color of lights used to outline taxiways and illuminate digital instrument panels, according to a report in The Boston Globe on October 28, 1998.

In addition to visual disturbances, the FDA recommended that the drug be used with caution in patients with retinitis pigmentosa. In the same press release, Dr. Marmor also stressed that the long-term effects of sildenafil are unknown, including permanent changes in vision.

However, not all the side effects associated with sildenafil may be bad. In the June 1, 2000, issue of the New England Journal of Medicine, William Sponsel, MD, and colleagues from the University of Texas Health Science Center, San Antonio, reported that in 12 adults (10 men and 2 women) who received the recommended 50-mg dose of sildenafil "there were significant increases in pulsatile ocular blood flow (+29 percent, from 916 +/- 103 to 1185 +/- 158 µl per minute; P = 0.02) and contrast sensitivity (+34 percent, from 92 +/- 11 to 122 +/- 11 log units; P = 0.01) a mean of 110 +/- 8 minutes after the administration of sildenafil. Retinal microcirculation increased in seven of the nine eyes in which there were stable scans (+8 percent, P = 0.09)." The investigators also noted that none of the study participants reported any "subjective visual symptoms."

They explained in the Letter to the Editor that pulsatile ocular blood flow occurs because of cardiac synchronous filling of the choroidal circulation, in which most of the ocular blood volume is found. "The increase in pulsatile choroidal blood flow after the administration of sildenafil was probably due to dilatation of the choroidal vessels, because there were not changes in intraocular pressure or systemic pulse amplitude, which are other major determinants of choroidal blood flow," the investigators said.

As a follow-up to this, in a news story in the October 15, 2000 issue of Ophthalmology Times, Dr. Sponsel and his colleagues reported data from two patients suggesting that sildenafil may be useful to treat patients with age-related macular degeneration (AMD) because of this increase in choroidal blood flow. In one with progressive loss of pericentral vision, a large perimacular threshold elevation occurred, increasing from 14 to 23 decibels inferotemporally; the same patient had an increase in contrast sensitivity after sildenafil was administered (baseline values for the 1 and 4 cpd patterns were 5.8 and 44.0, respectively; 100 minutes after treatment the values, respectively, were 31.2 and 92.3). In the second patient in whom the upper visual field was absent, the pulsatile ocular blood flow increased from the pretreatment level of 1,550 ul/minute to 1,975 ul/minute posttreatment. The patient had been blind in that area and after treatment "he had fairly normal light sensitivity," according to Dr. Sponsel.

Dr. Sponsel noted that he is not advocating treatment with sildenafil for AMD at this time and that the results in the two patients are anecdotal; however, a controlled clinical trial that would determine if sildenafil is useful to treat AMD has been started.