macular degeneration, macular, diagnosis retinal pigment epithelium (RPE) – My Macular Degeneration Journey/Journal

Important Cells

You would think that after saying I was running out of ideas, I would have the good grace to actually run out of ideas and shut up. You should be so lucky!? [Lin/Linda: =I= should be so lucky! ::grin::]

A comment was made suggesting we may have fostered some misinformation. We have stressed the idea of retinal pigment epithelial (RPEs) cells supporting the photoreceptors in the macula so much we may have given some people the impression the RPEs are only under the macula. This is not true. RPEs are under all of the photoreceptors and support all vision, not just central vision.

Once again my very erudite source, Wikipedia (I did print out another article but it is long and involved and I can probably get three or four pages out of it. Do you really want that?) reports the RPE layer was first discovered back in the late 1700s, early 1800s. It was noted to be black in color in many animals but brown in humans. This is because this single layer of hexagonal shaped cells is chock full of – all together now! – pigment. The RPE layer wraps around the back of the eye and ends practically at the iris.

We have talked about a couple of the functions of the RPEs. They are there to feed and clean up after the prima donna photoreceptors – both central cones and more peripheral rods – that apparently cannot do things for themselves.

Something I had not heard of before but makes sense is RPEs, as the conduit from the bloodstream to the interior of the eye, are also the gatekeepers. RPEs are at least partially responsible for the immune privilege of the eye. Remember we talked about how the eye is such a great place to do stem cell experiments because the immune response is so weak? Part of that weakness is due to the great jobs the RPEs usually do. They block bad things entering our eyes from the rest of our system.

RPEs gather up scattered light to make images sharper. That also keeps the light from causing extra oxidative stress.

Simply put the visual cycle is the amount of time as well as all the steps it takes for pigment in the photoreceptors to be depleted and then build back up again. The RPEs do much to control this.

Lastly, the RPEs produce signalling molecules that ‘talk’ to different parts of the system. Lots of very important functions for a one-cell thick layer of cells.

Age-related macular degeneration is not the only condition that causes vision loss due to malfunctions involving the RPEs. A more common one you may heard of is retinitis pigmentosa (RP). Their losses start in the periphery and progress inwards. Those with RP go blind. That’s BLIND. Maybe we ARE the lucky ones.

Do I know why our deterioration generally stops at the macula? Nope, but I have it on good authority it usually does. Usually does not mean 100% guarantee. Just usually. It is the best that I can do.

written October 10th, 2017

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The Science Stuff

Now comes the science stuff. Your eye has an area that takes care of the background and an area that takes care of seeing the stuff that you really want to look at. The part that does the seeing of what you really want to look at is called the macula. It is part of the retina which is the inside back layer of the eyeball. The retina converts light and images into electrical signals that are sent to the brain—light into sight.

Click on the image to get a detailed explanation of the diagram

 

The macula is made up of the photoreceptors, rods and cones, and the retinal pigmentation epithelials, RPEs for short. There are other parts of the eye, but this is Age-Related Macular Degeneration for Dummies.

 

 

I am not a physician nor a scientist.  There is quite a lot of information on the Internet if you’d like more details.

According to what I have read, the photoreceptors have the important job of turning ‘light into sight’. However, they are somewhat prima donnas and not very capable of taking care of themselves. I refer to them as the Masters. The RPEs are the Servants. Their job is to do everything for the Masters that the Masters cannot do for themselves. The Servants (RPEs) go to the store (the blood vessels in the choroid) and bring home nutrients for their Masters (the photoreceptors). They cook up a concoction of pigments and feed their Masters. They also clean up after their Masters.

The photoreceptors are the Masters, the RPEs are the Servants who feed and clean up after the Masters.

The trouble comes when the Servants/RPEs are not doing their job anymore. One of the first signs of AMD is the presence of something called drusen.  My reading very nicely indicated that these are fatty, metabolic byproducts of the photoreceptors’ job of turning light into sight. Basically, it seems to me that they are piles of poop. These piles of eye-poop suggest that the RPEs are not functioning as they should.

When the RPE Servants don’t clean up the eye-poop, it piles up & creates all kinds of problems!

As the eye-poop builds up, the environment becomes more toxic to the Masters, the photoreceptors. The Servants, the RPEs, also are not doing an extremely efficient job of feeding their Masters. As a result, both the RPEs and photoreceptors start to die. This causes the vision loss.

The Masters and the Servants die.  That’s what causes vision loss in dry MD.

Written in February 2016. Updated September 2018.

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