Love Wikipedia

Just came back from walking the Beastie Baby. I use my monocular a fair amount on walks. There were several, large, black birds in the trees in a little woods. I used my monocular to see hooked beaks. That meant they were most likely turkey buzzards, carrion eaters. Hypothesis confirmed when the sweet, fetid stench reached me. There was a dead deer over the bank in the stream.

Turkey buzzards are amazing. Ugly as sin, but amazing. What I was able to smell at 15 feet, they have been known to smell from a mile away. Our friends with the Audubon Society tell us the turkey buzzards (aka turkey vultures) have the largest olfactory system of any of the birds.

Which has exactly nothing, nothing to do with AMD, but is an example of one of the distraction skills, thoughts. One cannot live (well) thinking of nothing but AMD and our collective predicament. Besides I think Fun Facts are fun!

But enough of the sideshow and back to the main event. I might – and that is a big might – have found an answer to my question about how many degrees of arc make up central vision. I found what I think is the answer in Wikipedia. And here I was looking in all those hoity toity profession journals expecting some help. Silly me!

Actually I got two answers. Neither is God-awful if you consider where I thought this condition was taking me, but one of the answers is significantly better than the other. The first, better, answer is central vision is 18 degrees of arc (refer to the image to the left; click here for a larger version). If you consider the outer rim of the macula to be the boundary between central and peripheral vision, 18 degrees of arc is central vision and what we might be expected to lose. That is 18 degrees out of a visual field of what I have read different places is pretty close to 180 degrees horizontally. That’s 1/10! A heck of a lot better than the total blindness I thought I was going to have.

The other one is 30 degrees radius, which is unfortunately – check my math – 60 degrees of arc (refer to the image to the left; click here for a version).  A point 30 degrees from the center was chosen because after the first 30 degrees acuity declines sharply. There appears to be some sort of dividing line there.  Color vision also significantly decreased around the same place on the retina. The article also suggests 30 degrees radius is where good night vision ends.

So, the jury is still out on this one but we are getting closer to a verdict. The amount of loss that can be expected from geographic atrophy appears to be – and remember this is total speculation on my part; I know nothing! – somewhere between 18 degrees of arc and 60 degrees of arc. Those number are either a tenth of a third of our visual fields. Again, not great but better than what I thought was going to be true blindness. A small reason for optimism perhaps.

Right answer? Danged if I know. If you are going to see your doctor any time soon, do me a favor and ask. I really am curious.

Next: coming soon!

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