NAION

Non-arteritic anterior ischaemic optic neuropathy and the treatment of erectile dysfunction -- McGwin et al. 90 (2): 154 -- British Journal of Ophthalmology According to this article:

"For men with a history of myocardial infarction or hypertension the use of Viagra or Cialis may increase the risk of NAION. Physicians prescribing these medications to patients with these conditions should warn them about the potential risk of NAION."

For many men, the benefits probably outweight the benefits. "I don't care if I go blind! Give me my Viagra!"