The character in question is a young-ish (twenties to thirties, possibly?) who notices she's starting to lose her eyesight, but hides this from her superiors to keep her job. I need something that progresses so it's believable that she would still be able to hide it, and still (even if it's a lucky shot at close range) shoot someone who threatens to shoot her, but within the next couple of years she would be using a cane to get around (though I guess some of that could also be attributable to her finally admitting to her vision loss). [ETA: It is perfectly okay if the cause of her blindness would also cause her death - the story is set in a sort of earth-like afterlife; she dies of unrelated causes not long after the shooting - a year or two at most, though the timescale is not all that imporant.]
I've looked into macular degeneration (starts too old), cataracts (too easily treatable; I'd prefer something irreversible), glaucoma, diabetic retinopathy, Leber's congenital amaurosis (starts too young?), and a tumour on the occipital lobe. I'm still not sure if one of those might work or if there is a possible condition I might have overlooked?