The SafeZone mirror by EVT mentioned earlier is really the ONLY mirror on the market that puts such a large mirror on a helmet or eyeglass mounting. There are bar mounted mirrors that are 2.25" like the SafeZone but they will be quite far away in normal use. I've tried both and prefer the EVT. That being said, no mirror made can make compromised eyes work better. I am not sure why the o.p. thinks a bigger mirror will work better than anything else if they have tunnel vision. I'm not sure we are really qualified to help.
I actually know the person who makes the EVT mirrors. They are available for a lot less money than is advertised on their website if you go to certain local retailers. Lastly, one does not use a mirror to help them not kill anyone. They use a mirror to help them not be killed by anyone. Millions don't use any kind of mirror at all and manage that objective. I ride while partially sighted but with orders of magnitude more vision than the o.p. I doubt seriously that I would ride at all if my visual deficit was greater than it is. There are much safer ways to stay fit. And I am certainly not impressed that, to date, nothing serious has yet happened to the o.p. Do you think the many, many departed souls we discuss in this forum were on their first ever outing on a bike when crap happened?