Objective: To assess changes in electroretinography (ERG) and other retinal function parameters during 6 months of daily use of tadalafil, sildenafil citrate, or placebo. Methods: Subjects were randomized to use of a placebo (n = 82), 5 mg of tadalafil (n = 85), or 50 mg of sildenafil (n = 77) daily for 6 months. Electroretinographs were recorded using the International Society for Clinical Elec- trophysiology of Vision (ISCEV) protocol and standardized ERG equipment at all 15 study sites. Other tests of ocular anatomy and visual function were performed at each assessment. Main Outcome Measures: The primary outcome was the average mean change for both eyes from baseline to endpoint in ERG b-wave amplitude using dark-adapted combined standard response to a bright ISCEV standard flash. Secondary endpoints were other ERG parameter changes, visual acuity, number of errors in color discrimination testing, mean deviation in automated visual field testing, and intraocular pressure (IOP). Results: No significant differences were found between treatment/placebo groups for the primary outcome, most other ERG variables, visual function, IOP, or anatomic assessments. The medications were well tolerated. Conclusions: No abnormalities in ERG or visual function and no treatment-related findings suggestive of drug toxicity are associated with daily administration of tad- alafil or sildenafil for 6 months.
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