AccessMyLibrary provides FREE access to millions of articles from top publications available through your library.
Erectile dysfunction (ED) affects up to 30 million men in the United States, including half of all men ages 40 to 70. (1) Some 7% of men ages 18 to 29 have some form of ED, as do 18% of men ages 50 to 59. (2) So, it's no wonder that Viagra (sildenafil, Pfizer), the so-called "little blue pill," is one of the world's best-selling pharmaceutical agents.
However, several studies have associated the drug with nonarteritic anterior ischemic optic neuropathy (NAION). (3-9) In June, Pfizer agreed to include the report of NAION on the Viagra label, even though the company said its own review of 13,000 patients found no evidence that NAION occurred more frequently in men taking Viagra than in men of similar age and health who did not take the drug.
Still, optometrists must know how sildenafil works and be aware of potential adverse ocular side effects. Here, we'll discuss the drug's mechanism of action and possible adverse effects.
Erectile dysfunction is defined as "the inability to achieve or maintain an erection sufficient for satisfactory sexual performance." (10) While not life threatening, ED may result in a withdrawal from sexual intimacy and a reduced quality of life. (11)
[FIGURE 1 OMITTED]
The etiology of ED typically involves both organic and psychogenic factors. (12) Almost any disease that alters the vascular, nervous or endocrine systems--including diabetes mellitus, hypertension, heart disease and depression--can increase the risk of developing ED. Smoking is another risk factor. Also, the risk of ED dramatically increases with age. (11)
Penile erections involve the coordination of psychological, neurological, endocrine, vascular and muscular components. Tumescence, the vascular filling of the corpus cavernosa (cavernous bodies) of the penis, relies on neural and hormonal mechanisms that operate at various levels of the neural axis. The brain gathers information from a particular stimulus (touch, smell or visual) and sends that information to the base of the spine. There, primary nerve fibers that connect to the penis regulate blood flow during and after an erection.
Specifically, blood flow regulation depends on the relaxation and constriction of the smooth muscle of the cavernous bodies, which react via nitric oxide (NO) and cyclic guanosine monophosphate (cGMP). During sexual stimulation, the NO-cGMP pathway facilitates the relaxation of smooth muscle, thus increasing blood flow while closing venous drainage channels. The cavernous bodies become full and rigid, resulting in an erection. (12)
Therapies for ED include sexual counseling, external vacuum devices, vasoactive injection therapies, penile implants and oral medications such as sildenafil. Newer, similar medications include …