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All right, next topic:
ocular misalignment.

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If the eyes aren't aligned properly,

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then you might have an exodeviation;

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exo just means outwards,

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or an esodeviation, that's inwards.

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There's also a hyper and a hypo:
up and down.

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So let's give a couple examples of this.

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Let's say you have normal eyes,
and one of the ways

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you can actually estimate
if a young child

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has an eye that's turning in
or turning out,

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is by using the Hirschberg test.

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The idea is you shine a light
at the eyes,

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and you look at the light reflex,

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the corneal reflex of that light
bouncing off the eye,

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and you compare its position
to the underlying pupil,

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and normally that reflex ought to be

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laying right on top of that pupil.

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However, if you have one eye
that's deviated,

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for example, this left eye
is turned inwards,

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it's a left esotropia, then you can see

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that the light reflex is not quite over

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the pupil like it's supposed to be.

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In this case, the right hypertropia,

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the right eye is up a little bit,

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and you can actually estimate
the amount of deviation;

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and the rule is for every millimeter

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that this light is off center,
so in this case,

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if this was one millimeter
off of the pupil,

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equals about seven degrees
in misalignment, or 15 prism diopters;

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and this is the measurement
that we actually use

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in clinic, prism diopters.

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So we'll go over prisms in a second,

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but the Herschberg test, very useful.

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Now, we just talked about eso/exo,

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tropia/phoria, what does that mean?

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Well, tropia is when the eyes
are always deviated.

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So, if you have an exotropia,
that means that the eyes

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are deviated out, they're wall-eyed
and they're always deviated.

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Now phoria, on the other hand,

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just means that they're only deviated
sometimes.

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So, example of a tropia

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would be exotropia or esotropia,

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and of course, the hyper and hypo.

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And of course, of the phorias,

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we would call it something like
an exophoria,

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an esophoria, etc, etc.

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So let's show an example of this:
this eye,

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looks like this left eye
is deviated outwards,

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and we use our paddle to cover the eye;

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this is called the cover uncover test,

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and you look for this eye movement,
and that tells you

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that it's there all the time.

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So no eye movement here,

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because it looks like the right eye
is the dominant eye,

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this is a left exotropia.

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So let's try to correct it,
and to do that,

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we use prisms to try to get things
back in alignment.

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Things are still moving, so this isn't
quite enough prism

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to get things back in alignment.

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Let's try 20 diopters, and now,

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when you do our cover uncover test,

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we can see that things
are back in alignment.

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This was a left exotropia,
approximately 20 degrees,

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20 prism diopters, that is,
and you pick the tropias up

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with the cover uncover test,
which is what we just did.

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So let's try this one.

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These eyes look like they're
in reasonably good alignment.

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So let's do our cover uncover test.
No movement.

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Things are still nice and stable.

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Let's try the other eye; cover, uncover.

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Things are still in perfect alignment,
wonderful.

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But watch this: we'll do a cover

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and we'll do a cross cover test,
look at that eye move--

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Oh, it's moving again-- Oh, that one's
moving.

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This is what we call phoria,

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it's there some of the time,
basically when we break fusion.

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Let's see if we can get rid
of this for you.

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Yep, about 10 diopters a prism
is all it took to fix this phoria.

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So this was an exophoria.

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It's there only some of the time,

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and there was about 10 prism diopters
of it.

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You pick up phorias with
the cross cover test,

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completely different than
the cover uncover test.

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Okay.

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So this is a loose prism,

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and certainly with kids, loose prisms
are the way to go.

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They also make prism bars,

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basically put a bunch of prisms
in a single bar,

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and you just dial this thing up and down

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till you find the right amount
of prism to correct.

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I personally hate these bars,
I like to use the loose lens prisms,

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they're a lot easier to use;
my own personal preference.

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Certainly with children, you want to use

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the loose lenses
because they're smaller.

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If you use something this big,
kid's gonna try to grab it,

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it's not gonna work well.

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And if you have a tropia
that can't be corrected

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by correcting with glasses or patching,

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then you can always go to surgery;

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And basically, when we have eyes
out of alignment,

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we get them back in alignment,

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and we do that by either shortening

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or lengthening the rectus muscles.

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In this case, this rectus muscle
is cut off

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from its insertion and it's reinserted

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back onto the sclera using suture,
and this basically lengthens

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the effective length of this muscle
and gets things back in alignment.

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And you can do the opposite,
you can also shorten the muscle

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and reattach it back to
its original insertion.

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Not an easy surgery to do,
because you. could imagine,

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you're trying to do a scleral pass here

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and not perforate into the eye
and hit the retina,

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and the sclera is very, very thin.

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I mean, so thin. We're talking about
a third of a millimeter

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right underneath this muscle insertion.

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You can very easily perforate
into the eye,

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and not an easy surgery,
but very effective.

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So that was ocular misalignment.
Let's move on.