Addressing widespread apprehensions about the popular impotence medications, like Viagra and Cialis, in a company-funded study, the US researchers came to the conclusion that the use of such erectile dysfunction (ED) drugs did not have any noteworthy vision-related side effects on the otherwise hale and hearty men during a six-month testing period.

Pfizer Inc's Viagra or sildenafil and Eli Lilly and Co's Cialis or tadalafil belong to a group of drugs called "selective phosphodiesterase type 5" (PDE5) inhibitors, which treat ED by increasing the flow of blood to the genitals. However, there have been reports that the use of the drugs has resulted in blurred vision, blue-tinged vision or altered light perception in some men.

To test the findings, a research team Indianapolis' Lilly Research Laboratories conducted a randomized study of 244 healthy men or those with mild ED, aged 30 to 65 years, and having no vision-related problems. Out of these, 85 were administered 5 milligrams of Cialis, 77 were given 50 milligrams of Viagra, and the remaining 82 men took an imitation pill, everyday for six months.

Before, during and after the treatment, the men underwent thorough eye exams - including electroretinography, a test that measures the electrical response of the light-sensitive cells in the eye - and researchers found "no cumulative damage or effect of clinical significance" in 194 men!