Injections of other medications, especially steroids but even fillers, can enter a blood vessel and result in embolization or thrombosis of a vessel. It this were to occur to the central retinal artery, then it COULD cause blindness. However, this would be very difficult to accomplish unless you were injecting deep into the orbit, or trying intentionally to inject into another artery that supplies this area. None of the superficial facial or forehead vessels do this, and so injection of material into these areas is considered safe practice. And while these concerns may exist for other materials, the theoretical risk of Botox causing a similar problem is even lower. Even though Botox has been shown in animal studies to transit the nerve via axoplasmic transport and end up in the cell body in the central nervous system (CNS), the amount of Botox that can make it to the CNS is miniscule and there has never been shown to be any real impact of this phenomenon. Also, it has never been shown to occur in humans anyway.
I have never heard of Botox causing blindness. I do not even think this is a theoretical consideration based upon common injection areas. However, with filler, it is a different issue and has been reported and is theoretically possible of filler is inadvertently injected into a retinal blood vessel.
