Eric Wooltorton has published in the Canadian Medical Association Journal ( CMAJ ) a review of visual loss associated with use of Viagra ( Sildenafil ), Cialis ( Tadalafil ) and Levitra ( Vardenafil ).

Phosphodiesterase type 5 ( PDE5 ) inhibitors are drugs used to treat erectile dysfunction that have been recognized to cause temporary, minor visual changes in less than 10% of users.
However concerns were raised in 2005 after a small case series was published describing several Sildenafil users who experienced sudden, severe visual loss.

In July 2005, the FDA ( Food and Drug Administration ) has approved new labeling for Viagra, Levitra, and Cialis regarding postmarketing reports of vision loss related to NAION ( non-arteritic anterior ischemic optic neuropathy ).
Most, but not all, of these patients had underlying anatomic or vascular risk factors for development of NAION, including: low cup to disc ratio ( “crowded disc” ), age over 50, diabetes, hypertension, coronary artery disease, hyperlipidemia and smoking.
As of May 18, 2005, a total of 43 cases of ischemic optic neuropathy ( ION ) among patients using PDE-5 inhibitors have been reported to the FDA’s Adverse Event Reporting System. Since approval, 38 cases have been identified in association with Sildenafil, 4 cases have been identified in association with Tadalafil and one case has been identified in association with Vardenafil.
Most of these cases ( 25/43 ) appear to be the non-arteritic anterior ischemic optic neuropathy ( NAION ) subtype.
Thirty-six of the 43 cases reported accompanying visual loss, and 26 of these 36 cases reported the visual loss as continuing or permanent.
The majority of Sildenafil cases ( 21/38 ) appear to be cases of NAION.
Thirty-one of the 38 cases reported accompanying vision loss that was continuing or permanent in 22 cases. Visual loss was not documented in the remaining 7 cases.
In nineteen of the 38 cases, diminished vision or vision loss was reported from “immediately” after to 36 hours after Sildenafil administration.

Health Canada recently issued a warning that NAION has been reported in users of all the PDE5 inhibitors.
As of October 31, 2005, there have been 5 Canadian cases of visual problems that may have been possibly related to an erectile dysfunction medication. However, a causal link between the use of Cialis, Levitra or Viagra and NAION could not be established.
Individuals who have erectile dysfunction often have other conditions that put them at risk for NAION.

The cause of NAOIN is unknown, and it is unclear why a vasodilator might cause such vascular damage.
Other medications associated with NAION include Sumatriptan ( Imitrex ), Amiodarone ( Cordarone ) and nasal decongestants.

Patients who are prescribed PDE5 inhibitors should be informed of the symptoms of NAION and advised to discontinue usage and seek medical attention promptly if vision loss develops.
For patients who have had a prior episode of NAION, the potential risk of recurrence should be fully discussed before a prescription is issued.

Source:

1) Canadian Medical Association Journal, 2006

2) FDA, 2006

3) Health Canada, 2006


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