Slogging Through Again

I am waiting for my ride to go hot air ballooning and working on deciphering an article Lin sent me. Once again the question is how much loss can we expect from dry AMD, especially geographic atrophy? Regillo told me 60 degrees of arc loss would be extreme but my local retinologist said some people in their 90s can have GA encompassing the entire retina. Ouch.  [Lin/Linda: Sue wrote about ‘degrees of arc’ in her page Love Wikipedia.]

So, here be me again, slogging through another article I about half understand. Want to slog along? I would appreciate the company!

The article is entitled Clinical Endpoints for the Study of Geographic Atrophy Secondary to Age-Related Macular Degeneration published October, 2016. You there in the home audience feel free to download it and play along!

First of all, I latched on the statement (paraphrasing) “drusen may not result in actual visual acuity loss but the effects of having drusen can be seen in functional deficits very early in the disease process”. What functional deficits?

A 2008 paper by Feng Qiu and Susan Leat found people with very early AMD have loss of “low spatial frequency static contrast sensitivity”. Yippee. Once more down the rabbit hole. It appears – according to the appendix of Emergent Techniques for Assessment of Visual Performance – spatial contrast sensitivity has to do with lighting, the place on the retina where the image is falling and something called field size as well as time factors and the orientation of the image.

Boiled down it has something to do with how sensitive we are to variations in the data our eyes are gathering. I think. Don’t hold me to it. Just know that 20/20 vision with drusen might not be as perfect as we might think.

We talked about reduced dark adaptation before and this is also a problem in early AMD. Apparently there are several effects early drusen have that have nothing to do with acuity.

The next thing I had to look up – in the same paragraph, mind you! – was information that might help me understand a statement suggesting advancement to GA from early AMD may in part depend upon the presence of “reticular pseudodrusen”. So now we have drusen impersonators????

According to Association of Pseudodrusen and Early Onset Drusen by De Bats, Wolff et al (doesn’t that team sound perfect for the Halloween season?) pseudodrusen form on top of the RPEs and not below them as do ‘real’ drusen. There seems to be a connection between having ‘eye poop’ aka drusen on top of the RPEs and early and rapid develop of advanced AMD.

And the above was all in one paragraph! I may be a very long time in deciphering this baby.

So what I have discovered so far is this: visual acuity does not tell the whole story about functional vision loss when it comes to early AMD. If you have drusen be aware your contrast sensitivity and dark adaptation are probably already compromised. Secondly, pseudodrusen, which is eye poop on top of the RPEs, can predict a more rapid and earlier progression to GA.

Have I found a thing about GA outside of the macula? Not yet, but I am still reading! Talk at ya later!

written October 7th, 2o17

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