00:02
Alright, as we continue our crusade
through various pathologic disorders
involving the anterior
chamber and uvea,
we're going to look at how
we control the pupil's,
pupillary control,
whether they constrict or dilate.
00:15
And some of the disorders,
which are kind of interesting.
00:19
All of this is interesting, of course,
but this is particularly really cool.
00:22
Alright.
00:24
So this is where we're looking at,
we're going to be paying attention
to how the iris moves.
00:28
Remember, the iris is not only
heavily pigmented to limit light
to just going through the pupil
but it's also got a fairly high
investment of smooth muscle
and the smooth muscle is
in two concentric rings,
there are some that is radially
distributed that allows
the eye to dilate.
00:48
And then there are some that
is concentrically oriented,
allows it to constrict much
like a camera diaphragm.
00:54
Okay.
00:55
So a normal pupil is that.
00:58
A constricted pupil
is called miosis.
01:01
And that is that
inner circular layer
that is undergoing a contraction
of the sphincter pupillary muscle.
01:09
The Innervation is
parasympathetic.
01:12
So this is driven through
the acetylcholine receptors,
particularly the
muscarinic receptors.
01:18
Okay,
so that's a constricted pupil.
01:20
On the other end of the equation
is the dilated pupil, or mydriasis.
01:25
And the mydriasis is a contraction
of the dilator pupillary muscle,
which is radially oriented.
01:30
So you can see the little
arrows all the way around
which will pull the pupil
open by causing contraction
of the smooth muscle
cells there in the iris,
that innervation is sympathetic.
01:42
So this has implications.
01:44
When you are excited,
your pupils are dilated
because of epinephrine.
01:49
And we can also cause dilation of
pupil through a variety of drugs,
including many that are illicit.
01:56
But tropicamide
is a compound that
we put into the eye
that will actually be a
muscarinic receptor antagonist
and antagonizes the miosis
and the eyes dilate.
02:09
We do that so that we can
get nice wide open pupils.
02:13
And we can see into the fundus.
02:15
And so when you go
for your eye exam,
they will typically put some of that
topical tropicamide into your eye.
02:21
And we'll get a
nice dilated pupil,
that's also going to make
you a little photophobic
because you can't contract it
for about a half hour afterwards.
02:30
One other interesting
historical point,
it used to be thought
back in the Renaissance
and in some of the areas
around that period of time
that women with big dilated pupils were
beautiful, it was a sign of beauty.
02:44
And so they learned or was discovered is
that you could put a little belladonna,
which is a muscarinic receptor
antagonist in your eye
and it would dilate up.
02:52
Of course,
you couldn't see a damn thing
because you're very photophobic,
but you look beautiful.
02:58
Alright, so now you know
much more than you wanted
to know about miosis
and mydriasis.
03:03
How is this working?
How do we get?
So there are different things that
we also need to consider here.
03:09
In terms of the
neuronal control of this
because when one eye
constricts to a light,
usually the other one does too.
03:18
So there's a pupillary
light reflex.
03:20
So we have a right
eye light stimulus,
indicated in green.
03:26
And that's going to travel
down the optic nerve
going all the way back into
the superior colliculus,
that's the segment of brain
that's described there.
03:33
So this is kind
of high midbrain.
03:36
And in the superior colliculus,
that information that light is
coming in through the right eye
come in through the optic nerve is
transmitted to the pretectal nucleus.
03:47
And then...
03:49
where we get now combined
information to both eyes
it goes out to the
Edinger-Westphal nucleus,
which then has tracks that go
out along the oculomotor nerve.
03:59
So cranial nerve number three,
that will impact on or
impinge on the ciliary ganglia
and cause constriction.
04:08
And not only that,
but it's constriction in both eyes,
even though one is
being stimulated.
04:12
So we see miosis in both eyes,
that's the normal
pupillary light reflex.
04:18
Beautiful.
04:19
Rewind that again and run through
it, but it's really cool.
04:22
Now we're going to mess that
up in a couple different ways.