I too have a cat whose eyesight I question. The Vet has done some casual tests
& looked into her eyes with a flashlight in the dark, and has pronounced her
'normal'.
I think it is odd that this cat can walk past a glass door (inside) and not
notice or react to a flock of birds feeding on the other side (outdoors), even
when they are only six inches from her nose. Her sister goes ballistic over
those birds. The Vet suggested it might be a "mentation" problem, like maybe a
brain tumor. I severely hope not!
If a cat is kept strictly indoors & can find the foodbowl & the litterbox,
poor eyesight isn't the end of the world, I guess.