Definition: NAION (non-arteritic anterior ischemic optic neuropathy) is a sudden problem with the optic nerve, which links the eye to the brain, that can cause loss of vision. It is a listed warning on PDE5 inhibitor labels such as Viagra and Cialis, which say sudden vision loss may be a sign of it.
The Viagra label (section 5.3) says to stop all PDE5 inhibitors and seek medical attention if there is sudden loss of vision in one or both eyes. It says people who have had NAION are at higher risk of it again.
The label reports two observational studies that suggested about a 2-fold higher risk of NAION right after PDE5 inhibitor use:
| Study | Risk estimate (95% CI) |
|---|---|
| Observational study 1 | 2.15 (1.06 to 4.34) |
| Observational study 2 | 2.27 (0.99 to 5.20) |
The label says these studies do not establish cause.
A risk estimate of 2 means about twice the risk seen otherwise, in those study groups. The range in brackets is the 95% confidence interval. In the second study it starts just below 1, which means the result could also fit no added risk.
The studies looked at the time right after a dose. A log with dose times lets you show a clinician how soon after a dose any vision change began.
Read more on Dose Track: Viagra side effects · Cialis side effects