Apparently there have been rare reports of blindness among some users of Viagra:
http://news.yahoo.com/s/ap/20050527/ap_on_he_me/viagra_blindness
Now there’s a poser. Would you use Viagra to get an erection if you couldn’t without it, but there’s a chance that if you do you’ll lose your eyesight?
Can I just use it until I need glasses? 
I saw that report on the TV news this morning. They said 20 cases of blindness though and that article says 42. Hmmmm you would think it would be easy to get the number right.
The comment was made that there have been over 13 million uses of Viagra and 20 cases of blindness is a really small number to indicate any relationship. However, the doctor they interviewed did mention an eye doctor can examine your eye and tell easily if you have the ocular structure that might cause a problem. Apparently it is only people with a certain ocular structure that may be at risk. So if you are worried, it’s easy enough to get checked out.
And on the Today Show this morning, I heard fifty. Maybe it’s a spontaneous, temporary blindness.
“If your erection lasts more than 4 hours, go to the emergency room. Do not take matters into your own hands, as it were.”