Blind dog flinching on walks

I have a 13 year old Pomeranian with diabetes and cataracts. He can discern light and the absence of light but that's about it. He's been pretty good at navigating his environment for four years now. Certain things would always cause him to flinch, like sharp noises. But recently, about three weeks ago, the flinching started to occur his during walks, and it's more extreme, to the point where I think he is hurting from all the stress. What seems to trigger it is light and shadow. I have seen him flinch when I turned off the lights. He might think there's an object heading towards him.

Nothing in the environment has changed, he's been here for two years now, same building, same walks. He is not sensitive to bright lights. Also, he flinches more if he touches certain items inadvertently, like flower pots outside.
As soon as I noticed these flinching episodes, I took him to the vet and he got a checkup with no issues found. Since then though, the flinching has been getting worse. It's like everything scares him. I don't think it's pain, he is not bothered by bright stationary lights.
I've been limiting his walks and trying to avoid sunlight, but sometimes it even happens in the hallways of the building.
I'd like to restore his quality of life.With diabetes, exercise is very important and I think walks helped. Since the flinching started, he also doesn't want to walk far even when it's darker outside and the sun is not a factor.