Although open carry of a firearm (most anyway) is legal in Virginia, I would suggest against it. If I knew you had a gun I would plan to get it away from you. You will also stick out like a sore thumb in a crowd. People will point at you, and you may get stopped and questioned by police. You don't want to bring attention to yourself. That is the importance of concealed carry. Surprise is in your side.
You mentioned vision problems. If you can not pass the firearm test required for a concealed carry permit then don't consider carrying a gun around in public.
I take it you are not in a wheel chair anymore. How ambulatory are you? Can you swing a club? Cold Steel makes a few walking sticks that might interest you. You might also make use of them as a legitimate walking
aid.
The best way to prevent yourself from being a target is not to act like one. Don't put yourself in a situation where you are likely to be victimized. Be aware of your surroundings. Listen to the little voice inside your head. If it says cross the street to avoid that group of young thugs then cross the street. Don't go in the bad neighborhoods, even if it means a shorter walk to the bus stop. Don't wear headphones when you walk around, listen to what is going on around you. Limit the amount of times you have to be out at night.
When can you act? As others have said, when you fear for your life you may act in the preservation of your life. Virginia is not one of those states that require you to retreat from a threat, although clearly if you can safely retreat that is the best course of action. For instance, you are unlocking your door and someone comes up behind you and demands your money. You see that he is not armed, and you have the door unlocked. If you think you can retreat inside your home and get the door shut and locked without the bad guy getting in behind you than do it.
There are two basic requirements that have to be present before you can take action against an aggressor. First, they have to express their intent to do you harm. This expression can be with words, or with physical means. Second, they have to commit an overt act in furtherence of that intent. Say someone approaches and says to you "I'm gonna kick your but." Then they just stand there and make no actions that further their intent to beat you up, then you can not wack them over the head with a walking stick. But, if they take a step toward you, after declaring their intentions to harm you then you can take action to defend yourself. Both the intent and the overt act can occur at the same time, such as with a physical attack upon you. Say someone just comes over to you and starts beating on you without saying anything. The implication exists that he has the intent to harm you because that is what he is doing. Additionally, the aggressor has to have the capability to actually carry out any threat. For instance, say you were behind a secure door. A person outside said he was going to kill you and started hitting the door with his hands. He is not making any progress getting through the door, but still says he will kill you. He can not carry out the threat, so you can not pull out a gun and shoot him through the door.
Stun Guns: I have two issues with them. One, they don't work on everyone. Some people just have natural resistance, no matter what they tell you about overriding a persons nervous system. In a class of 35 of us who got hit with them there were 5 who did not go down. Two, you have to get close to use it. Might be ok as a backup defense, but I do not want to get that close to an attacker, just in case they have a knife.
Chemical or Pepper Sprays: Pepper spray generally works well, again, a certain percentage of the population will be resistant to its effects. There are other considerations with these as well, such as high winds, make them less effective. Potential to at least partially affect yourself is also high with these sprays.
Dogs: Some dogs will protect you, some won't. It is easier to predict what some dogs will do based on their breed but that is not 100%. Most bad guys probably won't be afraid of any dog that is smaller than a German Shepard or Lab size. My wife and I used to have 2 Great Danes, a gentle breed but also known for its fierce protectiveness of its owners. They were great as a visual deterrent. One would have given his all to protect us. The other was a rescue dog, and had some issues and was skittish.
If you do get in a situation where you have to defend yourself, call the police as soon as possible. If there are any other witnesses try to get them to hang around or at least get their names/phone numbers. Don't lie to the investigators, they can usually confirm your story through physical evidence. File charges against your attacker.
If you don't call the police here is what might happen. You will get attacked, then club the attacker and split his skull. You go home and don't call the police. Bad guy goes to the hospital. The ICU nurse will call the police, and they will respond. They will hear his side of the story, no doubt about how you clubbed him like a baby seal for no reason. They will come looking for you as if you were a suspect, because that is all they know is his side of the story. That, and because of the old addage that honest people don't run when they have done nothing wrong. You may get arrested, and brought to the station for questioning. You want to be the first one to call the police.
I've written a lot, and I probably haven't covered all the bases. You are on this forum, so I am assuming you have a good bright flashlight for blinding any potential attackers.