00:01
Welcome to this presentation
on the visual pathway.
00:08
The first topic that
I'm going to guide you through
on this journey
along the pathway
is the passage of light
through the various components
of the eyeball.
00:21
And this is necessary
to focus the light
on the phobia centralis
the point at which we have
the greatest visual acuity.
00:29
The first structure
that light will pass through
is that of the cornea,
which you see labeled here.
00:38
Next, the light will pass through
the aqueous humor.
00:43
And then through
an aperture of the iris
that we call the pupil.
00:48
And you see that opening
labeled here.
00:51
The lens is the next structure
through which light will pass
along it's travel.
00:56
And then its greatest journey
is going to be through the
vitreous humor.
01:01
And then the light will hit
the retina.
01:05
And by striking the retina
photoreceptor cells
will become activated.
01:13
At this slide depicts
the major layers of the retina
that will allow
the visual scenes
to be delivered
through the optic nerve.
01:25
First, the pigment epithelium
is shown here.
01:30
This is the external most component.
01:34
The purpose
of the pigment epithelium
is to absorb any scattered light,
which helps with visual acuity.
01:42
The photoreceptors
are shown here.
01:45
And we have cones and rods
in through here.
01:49
And we'll speak to those
in detail shortly.
01:54
From here, photoreceptors will
activate stimulate bipolar cells.
02:03
And then the bipolar cells
will communicate and activate
ganglion cells.
02:10
And then the axons
from these ganglion cells
will then form the optic nerve.
02:16
And the optic nerve is forming
right here
on the right upper portion
of this image.
02:23
Now, let's take a look
in greater detail
about the photoreceptors.
02:30
First, we have the rods.
02:33
And here's a nice illustration
demonstrating the rod.
02:42
And then the cones
are shown here
at least one cone
And you can see this cone shaped
appearance here
to the outer segment
of this photo receptor.
02:56
Now, let's describe the functions
of the cones and the rods.
03:04
The cones are
located specifically
within the fovea centralis
exclusively,
there are no rods at this place.
03:12
As you move outside of the
fovea centralis
you're within the macula lutea.
03:17
The cone density will start
to decrease
and then rods
will start to increase in density.
03:23
And then once you get
to the periphery
of the macula lutea
then you have exclusively rods
in the peripheral aspects
of the retina.
03:35
Cones are necessary
to operate in bright light.
03:41
They are responsible
for conferring color vision.
03:45
And in order to do so
there's a population of
red, green, and blue cones.
03:51
They are responsible for
high visual acuity.
03:56
And if we have an
excessive loss of cones,
this is a cause
of legal blindness.
04:07
Rods which start to show up
outside of the fovea centralis
and then we see them exclusively
outside of the macula
are responsible for
low light vision.
04:23
As a result,
they have poor visual acuity
and they are responsible,
for a chromatic vision.
04:31
So we see
scales or shades of gray
and not color.
04:36
And excessive loss of rods
impairs our ability to see
in low light or during nighttime
does this can be a cause
of night blindness.
04:52
The retina in certain situations
can become detached
And when that happens
there is a separation of the
neuro retina,
which would be the boundary
between
the photoreceptors
and the pigment epithelium.
05:14
As a result to this separation,
the neural retina
from the pigment epithelium
blood supply to the
photoreceptor cells is disrupted.
05:23
The blood supply to this area
is from blood vessels that reside
in the choroid
which will be down
in this area here.
05:32
And so you are dependent then
on the diffusion
of the components from the blood
to maintain the viability
of the retina
that becomes lost
when we have detachment.
05:45
Possible symptoms are
a shower of pepper or floaters
as visual sensations.
05:51
This is do extravasated
red blood cells
that came from a disruption
of the blood supply.
05:56
You may also see flashing lights,
or a shadow, or curtain
over the field of vision.
06:02
The retinal detachment can result
from different causes.
06:06
The most common one is
rhegmatogenous
retinal detachment,
which is a structural collapse
of the vitreous humor
that pulls the retina away
from the
retinal pigmented epithelium.
06:17
Then there's a
tractional retinal detachment
where scar tissue exerts
tractional force
and is pulling the retina away from
the retinal pigmented epithelium.
06:28
This may be seen in diabetes
for example.
06:31
Another cause is
exudative retinal detachment.
06:35
In this case,
fluid leaks from blood vessels
and separates the retina.
06:40
It may be caused by
inflammation
or abnormally
leaky blood vessels.