Whether your branch artery occlusion was caused by the Restylane injection or not, this is a terrible event. It sounds like you are getting very good care for this and I advise you to carefully follow the recommendations of the retina specialist.
Periocular injection of certain materials is a known risk for embolization into the retinal circulation. Certain injection locations and materials are at increase risk of causing retinal branch artery occlusion. This occurs when material is embolized into the retinal arterial circulation. The damage to the retinal circulation, which provides the blood supply to the retina, varies depending on where the embolized material lodges. When this in closer to the main supply of blood, more of the retina and the vision is affected. When the material lodges more peripherally, less of the retina is affected. When the circulation to the macula is affected, the visual loss is most profound, which is consistent with your situation.
There are other causes of branch retinal vein occlusion. This included embolization of fat, atheroma from hardening of the arteries, and other materials. You situation is somewhat unusual because you did not develop visual loss at the time of treatment. The fact that this type of visual loss is very rare does not diminish the impact of this loss to you. Injection of the glabellar area is associated with the highest risk of retinal embolization due to the vascular organization in this area. For this reason, many experienced injectors wouldn't treat this area or will limit treatment of only high intradermal placement.
Local disturbances in circulation following injection of HA fillers to the nose and parts of the face have been successfully treated with massive local injection of hyaluronidase, the enzyme that breaks down hyaluronic acid, the sugar gel these filler are composed of. However, the soft tissue of the face is much more tolerant to relative or absolute ischemia than the retina. The retina is part of the brain. Deprived of blood supply or sufficient blood supply, very quickly leads to irreversible damage. This is very much what happens to the brain in an ischemic stroke. I am not aware of any cases where retinal circulatory disturbance caused by HA fillers was successful reversed by hyaluronidase. To be of much help, this would need to be done within hours of the insult and this presumes that the occlusion was in fact the result of HA embolization. Now two weeks later, there would likely be no value to this.
Regarding your visual prognosis, much depends on the precise anatomic details. The macular structure called the fovea provides the finest vision that we rely on for reading, and resolving fine detail. This has been affected by the BRAO. What is not clear in your description is if this has been completely or only partially affected by the ischemia. It is possible that if it has only been partially affected, some of the central vision will improve as the swelling associated with the event improves. Your retina specialist will give you a better idea of this as he or she follows you.
If you have not done so, please consider writing up this experience for the "Real Experience" section. This will help others learn of this potential risk of glabellar and forehead treatment. Our thoughts and prayers are with you that your vision improves from this terrible loss.