(NBC News) – GLP-1 drugs may increase the risk of NAION, a rare optic nerve condition that can lead to sudden vision loss. It has no known treatment.

The Food and Drug Administration said Monday that GLP-1 drugmakers must add a warning label about a rare eye condition that can cause sudden blindness.

The condition, called nonarteritic anterior ischemic optic neuropathy, or NAION, affects the optic nerve, which carries signals from the eye to the brain. When blood flow to the nerve is reduced or blocked, it can cause sudden vision loss. The condition is permanent with no known treatment. (Read More)