I'm hearing...but still I never open the door unless I know who it is. But I'm wondering, since the OP is also low vision, and a peephole wouldn't help, maybe he could instruct his friends and family to knock in a certain way. For instance, 2 knocks, wait a few seconds, and then 3 knocks. That way he would know it was someone he knows.
If im home alone, I will answer the door and try to understand the person, if not ill just say sorry no and shut the door unless its the post or delivery.
That's the route I usually take, though if the person is questionable, I get shirtless (I'm muscular from past college ball experience), fill a big mug with beer, and answer the door for a "wut-da-hell-u-want" intimidating effect! LOL
I open my front door with a gun in my hand.......
I open my front door with a gun in my hand.......
And......if it was two Mormon Missionary boys, I would show up in my bathrobe with hubby on the side!
They never come back again although the one did.........