Fat transfer to forehead and blindness?

I read about risk of blindness from fat graft to the forehead. not sure the cause though. i've read says its because the needle cut a blood vessel that supplies the optic nerve & fat particles injected into the vessel or was from the fat putting pressure on the vessel. how often does it occur can some type of scan be done to map out blood vessel exact position in patients foreheadcto ensure avoidance 4)as time goes on if the fat graft grows can that increase the risk of later blindness