April 14 (HealthDay News) -- The erectile dysfunction drugs Cialis (tadalafil) and Viagra (sildenafil) didn't appear to damage vision in men who took the medications daily for six months, according to a drug company study.

These drugs, called selective phodiesterase type 5 (PDE5) inhibitors, treat erectile dysfunction by interfering with the action of the compound PDE5 in the blood vessels of the penis. But there are concerns that PDE5 inhibitors may also act on similar compounds in the retina, the part of the eye that receives and transmits images to the brain, according to background information in the study.

Men taking PDE5 inhibitors have reported mild and temporary blurred vision, altered light perception, and blue-tinged vision.

This Eli Lilly study included 244 men, ages 30 to 65, who were randomly selected to take either 5 milligrams of tadalafil, 50 mg. of sildenafil, or a placebo daily for six months. The men underwent thorough eye tests before, during and after treatment.

By the end of the study, the researchers found no significant differences in vision between the men who took the drugs and those who took the placebo. The findings were published in the April issue of the journal Archives of Ophthalmology.

"There are several reasons ophthalmologists need to be acquainted with the pharmacologic profiles of PDE5 inhibitors and their potential side effects," the authors wrote "The frequency of erectile dysfunction, which is a form of peripheral vascular disease that impairs men's abilities to achieve and maintain an erection, increases dramatically with age and in the presence of cardiovascular risk factors. Therefore, many men who take PDE5 inhibitors to treat their erectile dysfunction will also be followed up by ophthalmologists for ocular disorders such as diabetic retinopathy, macular degeneration and ocular vascular disease."

"Furthermore, PDE5 inhibitors can exert direct effects on the retina, and such effects probably account for many of the visual side effects such as blue-tinged vision and light sensitivity that have been reported," they concluded.

But they said their "results indicate that there is no cumulative damage or effect of clinical significance for either 5 milligrams of tadalafil or 50 milligrams of sildenafil taken daily for six months."

SOURCE: JAMA/Archives journals, news release, April 13, 2009