Shelter Dog Scared of Everything

Hello!

I recently saved a 10-year-old shelter dog (now named Pooka) who was kept outside and neglected his whole life. It's a long story, but the dog's owners suffered from health problems and were very neglectful. Pooka spent his whole life outside unmonitored, and he was even hit by a car twice! He never had designated food and only ate scraps the family threw outside from a bucket. As a result of his hard life, he is mostly blind and totally deaf. He also has some permanent damage done to his back legs which causes him to stumble sometimes. When the shelter found him, he was shivering in the rain and bloody from being hit by a car. His owner had died unexpectedly and Pooka had wandered off after not being fed for a few days. When I adopted him (he spent a month in a small cage in an open shelter subject to rain), he was unused to being pet, and would try to bite if startled (there was no meanness, he's just very scared).

I've had him for a month and a half, and he's made a lot of progress but Pooka is scared of everything (given his history, I understand why!) I've trained him to be pet, and to seek affection. He is mostly trusting with me (a woman) and my partner (a man), with whom he's much more hesitant. I'm worried because Pooka, seemingly with no stimuli, will start trembling and pacing. I've taken him for walks in the city, which he seems to enjoy, but he's also terrified at the same time. It's clear he needs more socialization and training, but I'm at a loss. Because of his disabilities, I don't know how to make training more efficient and socialize him better. I would appreciate any help or tips anyone may have!

A picture of Pooka, who really is trying to be a happy boy!