Biology of the human choroid

Published on April 27, 2016   30 min
Hello, my name is Robert Mullins. I'm a professor at the University of Iowa. And I'm going to be speaking to you today about the choroid.
Today, we're going to be discussing several points about the choroid, including a general overview of ocular anatomy as it pertains to the choroid, and very briefly we'll discuss retinal signaling and photoreceptor cells, and the fact that that process requires a large amount of oxygen consumption, the source of that oxygen in the form of ocular vasculature. I will then discuss briefly some of the physiological insights into the structure of the choroidal microvasculature. We'll spend some time reviewing the choriocapillaris. We'll discuss the groups of cells that exist in the choroid. And the development of the choroid will be our final point.
While it is obvious in one sense that the eye has an outside and an inside, the inner-outer axis is very important in describing one's position in the retina. And so what I've drawn here is a cartoon of an eyeball cut in crosssection, and you can see this line that denotes the inner-outer axis. Taking a small piece of the yellow retinal tissue and the brown choroidal tissue in the cartoon, we see the layers of the retina starting from the inside toward the outside where the choroid resides. And these layers have been, clasically, labeled based on this inner-outer access. So the innermost layer is the ganglion cell layer, innermost layer of nuclei. The next layer of nuclei is the inner nuclear layer, and external to that is the outer nuclear layer. And the outer nuclear layer comprises the nuclei of the photoreceptor cells, which also have an inner segment and an outer segment, again, positioned logically along this inner-outer axis as we've discussed. And external to the outer segments of photoreceptor cells, reside the RPE, the choriocapillaris, and the outer choroid. When light enters the eye, it passes through the cornea and the pupil in the lens and is focused on the retina, and a photon of light actually has to penetrate through all of these other retinal neurons before it reaches the outer segments of the photoreceptor cells where the light is converted into electrochemical signal. The photoreceptor cells then signal the bipolar cells in a mechanism that we'll very briefly discuss, the bipolar cells in turn signal the ganglion cells, which send an action potential out through the optic nerve and to the brain.