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

Next: Make the Safe Call

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