diminish the light that's getting to the retina.
And in the area of greatest sensitivity, the fovea, you want to take away
the components that are going to scatter the light,
absorb some of the light and diminish the sensitivity,
the accuracy of what you would be able to see were those elements not there.
That's why they are not present over in the foveal region.
So, let's look at this in some detail.
Here is again, a little piece of the retina.
And we're going to take this piece out diagrammatically and blow it up, and
look at the elements that are in the retina.
And let's look at that in a little bit more detail than in this picture.
So light is coming in here, and right away you see
something that is odd and seems an unusual arrangement.
And that is that the photoreceptors,
the cells that actually transduce the light by capturing photons and turning
them into the beginnings of the neural signals that end up going to the brain.
Are at the back of the eye, not the front and
the light therefore has to go through all of this junk.
Well, it's not junk.
It's obviously critical processing machinery, but
it has to go through all that stuff that degrades the light by scattering it,
by absorbing some of it before the light reaches the photoreceptors.
That's why these elements are taken away in
the phobias I told you a minute ago, but in the vast majority of the retina,
the light is passing through these other elements.
So why is that?
Well, the reason is that the photo pigment layer, which is here,
is an absolutely necessary component that has to be adjacent to the photo receptors.
The reason is that the photo receptors have a high metabolic rate and
the disks that contain the photo pigment molecules are actually
being turned over at a high rate and the disks are being degraded.
And that degraded detreiutus has to be dealt with and removed so that the rods,
and there are two types of photoreceptors that we'll talk more about in a minute.
That needs to be removed so
that they can continue to function on an ongoing basis properly.
That's the reason that the photoreceptors are in the back of the eye.
And the next question we should ask is well what are all these other cells doing?
First of all, there's a straight through pathway of light
that's mediated by bipolar cells that is basically the pathway that's
forming the high-resolution that one gets from vision.
But there are also these other cells that are integrating information