I adopted a 2 year old cat a few months ago and despite the slow introduction we're still having hissing issues between her and my existing cat. However, today I noticed when feeding her treats, she couldn't see her treat on my hand, and actually tried to gnaw my fingers which smelt strongly of her treats instead. But she is absolutely able to navigate the house and jump to her high spots perfectly. Oh, but when she is walking she doesn't seem to see things she's about to walk on and her favourite toys are noisy ones.

So now I'm wondering if this is the cause of their issues. My existing cat can often sneak up on her (I am getting her a bell collar tomorrow), even in a brightly lit room.