I've heard of them twisting their necks before they die, I believe that is caused by decreased oxygen to the brain, it seems to be a fairly normal thing before the bird passes away.
I'm no expert, so I'm just making observations here, but I'd guess he experienced faded or blurry vision, combined...
I'm so sorry for your loss, that sounds heartbreaking :hugs
What led you to believe he lost eye sight?
Standing still and not wanting to move sounds more like he was lethargic/uncomfortable.
What meds did you give him, and what dose? What is the feed, is it for laying birds, and do you offer...