My cat died, can someone help me figure out a cause?

My 8 and a half month old cat died today. I'm pretty sure he wasn't already right to begin with. He had vision problems a lot when he was younger and we had to take him to the vet to get eye drops. He always acted like he didn't have a sense of balance and acted like he was half out of it. He never meowed much at all and was very silent when he did. He acted like he wasn't all there in the head. A week before his death, I found him peeing on himself on my porch and I clapped and yelled and he didn't move or do anything, he still stood there completely still. He looked puny a lot. Does anyone have any ideas on what he could have died from or what was wrong with him?