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Comment by refurb | Hacker News Reader

It's also fascinating when the other end of the visual system (the brain) has issues.

My aunt had a very small stroke in her visual cortex. Incredibly it only impacted the visual processing in the upper right quadrant of the right eye. Everything else was fine.

She was telling me that the affected part of her field of vision wasn't black (as you'd expect). She described it as "empty". It just wasn't there. There were no good words to describe how that looked visually.

Interestingly as her brain recovered somewhat, the "empty" area got a bit smaller, then her brain started to do "error correction" and to her, the "empty" part is gone, but it doesn't provide any visual information. Similar to the tweets, it's just filled with "background".

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10+ years back a handful of times I suffered from (what I think were, but you’ve got me thinking) migraines that resulted in localized loss of visual perception. In my case the spot was right in the center of my field of vision.

The loss manifested itself at first as trippy vibrating colors, which soon changed to non-black nothing.

After that I would look straight at things not only to not see them, but to not even realize I am not seeing something.

https://en.m.wikipedia.org/wiki/Scintillating_scotoma

Sounds about right, good to rule out any sort of stroke… Though honestly that pulsating phase the article highlights was the least of my problems. For 10 minutes or so while it’s there you can at least tell something’s wrong, for the rest of the day it’s a treacherous blind spot that’s easy to forget about.

I've had these several times myself. For me, they start as a small "blind spot" at the center of my field of view, which was really scary, particularly if I was trying to read or do screen-work at the time. After the first one, the appearance of the rainbow zig-zags was actually comforting, because that confirmed what it was. Since I was effectively incapacitated for the duration, I'd just lie down and enjoy the light show.

It's been years since I had an occurrence, but the timing was pretty reliable.

~30 minutes: slowly growing blind spot at the center of my field of vision.

~15 minutes: rainbow zig-zags in a slowly expanding circle from the blind spot until it encircled my whole field of view, after which it faded out and I could focus pretty normally again. No headache during or after.

After multiple rounds, I figured out the, or a, trigger: absinthe. Drinking absinthe reliably brought one on ~18 hours later. Only ever had one that I couldn't tie to absinthe. Stopped drinking absinthe years ago, and the scintillating scotoma stopped as well.

That is very common. It's the classic migraine aura.

We also cannot see what's behind us, yet it doesn't feel black, just not there.

The exercise that made me perceive, what I think, is the closest to what's meant by that what's described as "empty":

1st step) Imagine you have eyes in the back of your head.

2nd step) Concentrate on trying to see what's behind you.

I’ve heard blind people (that weren’t born blind) describe it a similar way. “I don’t see black, I see with my eyes what you see with your elbow”

My dad had a small stroke that left him unable to see in one eye. But being neurological, this wasn't exactly like losing sight.

If someone sitting next to him spoke, and he wasn't facing them with his remaining working eye, he would be taken by surprise, and would not always understand who was talking to him. Instead of turning his head, he would frequently ask, "Who's that? Where are you?" It wasn't just that he couldn't see the person, it was almost as if the person wasn't there. He frequently described how the blind side of his vision wasn't black, just "not there".

Another oddity was that he didn't notice the loss of vision until maybe a couple of days after it happened.

The same thing happened to my mom after her stroke.

There wasn't a black spot in her field of vision, it was a kind of indefinite background that didn't stand out, but didn't have any information. Her best explanation is that it was like your peripheral vision, you can "see" things to the side, but you're not getting 100% of the detail you'd get if it was in front.

But yes, she said the same thing - it freaked her out when she would move her eye slightly and something that was hidden by the blind spot popped up.

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