Pfizer Inc's Viagra (sildenafil) and Eli Lilly and Co's Cialis (tadalafil) treat impotence by increasing blood flow to the genitals, but some users have reported blurred vision, blue-tinged vision or altered light perception.
The drugs work by blocking the action of the enzyme phodiesterase type 5 or PDE5 on the blood vessels in the penis. But PDE5 inhibitors may also act on blood vessels in the retina, which could explain some of the reports of vision problems.
To test this, a team led by Dr. William Cordell of Lilly Research Laboratories in Indianapolis conducted a randomized study to look for changes in the retina among men taking Viagra or Cialis.
"Our results indicate that there is no cumulative damage or effect of clinical significance," for the studied doses of either drug, they wrote in the Archives of Ophthalmology.
taken from : China Daily
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