Actually there are different types of canes, they differentiate to the severity of one's vision. A blind person would use a long cane with a circular, round tip compared to one who is partially blind that would use a shorter cane with a flat tip. Those which are shorter are basically used to advise and aware others that you have a partial visual impairment, but can still see, therefore they still meet the criteria for "canes", and shouldn't be considered a walking stick.
I also believe that Souta's cancer played a heavy role in Shu's disability, although I think it's primarily related to
symbolism. If it was the genome he would of been blind as soon as he injected it, but his face crystallized after he absorbed everyone's void including Souta's instead of solely Ayase's. He also would've mentioned it if he lost his vision so that was probably only an after effect of the amount of cancer he took on. I mostly found it as an excuse to portray this symbolistic message, but I can't prove that he lost one eye instead of both so I don't know what to rely on.
