Viagra and Vision

With an ex-Presidential candidate as its pitchman, more mentions on late-
night talk shows than Joan Embry and the dubious honor of being the world’s
top pharmaceutical treatment for impotence, few drugs in history have been
more in the public eye more than Viagra – or gotten more attention for
affecting the public's eyes. Along with its impact below the belt, Viagra
(sildenafil citrate) is well-documented to cause retinal dysfunction lasting
several hours after it is taken. Most commonly, it causes increased light
sensitivity, blurring, and a bluish tint or haze to vision in many men who
take the medication. Since receiving FDA approval in March 1998, Viagra has
been prescribed more than 22 million times in the U.S. alone and is available
in 90 other countries, according to manufacturer Pfizer. Here’s what you need
know about Viagra and your vision:

Who is most likely to get ocular side effects?
Viagra is available in three prescribed doses – 25, 50 and 100 mg pills. Side
effects are usually dose-related, meaning the greater the dosage, the greater
the risk. According to reports by Pfizer and subsequent studies, ocular side
effects occur in:

About 3 percent of men taking doses of 25-50 mg
About 11 percent taking 100 mg doses
About 50 percent of men taking 200 mg
Nearly all men taking 600 to 800 mg.

Why does Viagra cause vision changes? Viagra is effective on erectile
dysfunction because it inhibits phosphodiesterase 5 (PDE-5), an enzyme that
enhances the effects of nitric oxide, which is released during sexual
stimulation to relax the smooth muscle of the penis and facilitate blood
inflow. However, the drug also has a milder inhibiting effect on PDE-6, an
enzyme actively present in retinal photoreceptors. This causes an increase in
the concentration of cyclicGMP, resulting in a depolarization of the rod cell
– and increased light sensitivity and the infamous "blue vision."

When do side effects occur? The side effects are short-lived and generally
peak within 1-2 hours after the drug is taken. What is the long-term vision
damage? Hard to say, since the drug has been on the market for only a few
years. So far, no long-term retinal damage has been reported, but then again,
long-term electroretinograms (ERG) have not been done, says Michael F. Marmor,
MD, a Stanford retinal specialist who has published studies on the ophthalmic
effects of Viagra. He believes the drug could conceivably result in lasting
damage to photoreceptors, so he recommends that you avoid it if you have
macular degeneration, diabetic retinopathy, retinitis pigmentosa or other
retinal disease. (Meanwhile, Viagra's own label issues warnings to patients
with existing AMD or retinitis pigmentosa because they were not studied in
past clinical trials.)

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