Mild and transient blurred vision, blue-tinged vision and altered light perception have been reported by men taking these drugs, and some visual complications of long-term use have been suggested.
Viagra and similar medicines are known as selective phodiesterase type 5 (PDE5) inhibitors because they treat ED by interfering with the action of PDE5 on the blood vessels in the penis.
However, PDE5 inhibitors may also act on similar compounds in the retina, the part of the eye that receives and transmits images.
Of the chemicals, sildenafil citrate is sold as Viagra, tadalafil as Cialis, and verdenafil hydrochloride as Levitra.
William H. Cordell of the Lilly Research Lab and his colleagues conducted a randomised placebo-controlled study to assess changes in the retina among men taking tadalafil or sildenafil.
A total of 244 healthy men, some with mild ED, aged 30 to 65 were recruited. Of these, 85 were randomly assigned to take five mg of tadalafil, 77 to take 50 mg of sildenafil and 82 to take a placebo daily for six months.
The men underwent comprehensive ophthalmic tests, including electro-retinography (test to measure the electrical response of the light-sensitive rods and cones in the eye, used to detect diseases of the retina) before, during and after treatment.
Among the 194 men (79.5 percent) who completed the study, no significant differences were found between treatment and placebo groups on electroretinography, visual function tests, measurements of intraocular pressure (pressure within the eyeball) or assessments of the anatomy of the eye.
Nine participants (two in the placebo group, one in the tadalafil group and six in the sildenafil group) discontinued the study because of an adverse event, but only one of those was an ophthalmologic event (in the placebo group).
No abnormalities that would be suggestive of drug toxicity were observed in any of the participants, said a Lilly Research Lab release.
These findings were published in the April issue of Archives of Ophthalmology.
copyright 2009 by IANS.
impotence (ED) in men
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