All right, next topic: ocular misalignment.
If the eyes aren't aligned properly,
then you might have an exodeviation;
exo just means outwards,
or an esodeviation, that's inwards.
There's also a hyper and a hypo: up and down.
So let's give a couple examples of this.
Let's say you have normal eyes, and one of the ways
you can actually estimate if a young child
has an eye that's turning in or turning out,
is by using the Hirschberg test.
The idea is you shine a light at the eyes,
and you look at the light reflex,
the corneal reflex of that light bouncing off the eye,
and you compare its position to the underlying pupil,
and normally that reflex ought to be
laying right on top of that pupil.
However, if you have one eye that's deviated,
for example, this left eye is turned inwards,
it's a left esotropia, then you can see
that the light reflex is not quite over
the pupil like it's supposed to be.
In this case, the right hypertropia,
the right eye is up a little bit,
and you can actually estimate the amount of deviation;
and the rule is for every millimeter
that this light is off center, so in this case,
if this was one millimeter off of the pupil,
equals about seven degrees in misalignment, or 15 prism diopters;
and this is the measurement that we actually use
in clinic, prism diopters.
So we'll go over prisms in a second,
but the Herschberg test, very useful.
Now, we just talked about eso/exo,
tropia/phoria, what does that mean?
Well, tropia is when the eyes are always deviated.
So, if you have an exotropia, that means that the eyes
are deviated out, they're wall-eyed and they're always deviated.
Now phoria, on the other hand,
just means that they're only deviated sometimes.
So, example of a tropia
would be exotropia or esotropia,
and of course, the hyper and hypo.
And of course, of the phorias,
we would call it something like an exophoria,
an esophoria, etc, etc.
So let's show an example of this: this eye,
looks like this left eye is deviated outwards,
and we use our paddle to cover the eye;
this is called the cover uncover test,
and you look for this eye movement, and that tells you
that it's there all the time.
So no eye movement here,
because it looks like the right eye is the dominant eye,
this is a left exotropia.
So let's try to correct it, and to do that,
we use prisms to try to get things back in alignment.
Things are still moving, so this isn't quite enough prism
to get things back in alignment.
Let's try 20 diopters, and now,
when you do our cover uncover test,
we can see that things are back in alignment.
This was a left exotropia, approximately 20 degrees,
20 prism diopters, that is, and you pick the tropias up
with the cover uncover test, which is what we just did.
So let's try this one.
These eyes look like they're in reasonably good alignment.
So let's do our cover uncover test. No movement.
Things are still nice and stable.
Let's try the other eye; cover, uncover.
Things are still in perfect alignment, wonderful.
But watch this: we'll do a cover
and we'll do a cross cover test, look at that eye move--
Oh, it's moving again-- Oh, that one's moving.
This is what we call phoria,
it's there some of the time, basically when we break fusion.
Let's see if we can get rid of this for you.
Yep, about 10 diopters a prism is all it took to fix this phoria.
So this was an exophoria.
It's there only some of the time,
and there was about 10 prism diopters of it.
You pick up phorias with the cross cover test,
completely different than the cover uncover test.
Okay.
So this is a loose prism,
and certainly with kids, loose prisms are the way to go.
They also make prism bars,
basically put a bunch of prisms in a single bar,
and you just dial this thing up and down
till you find the right amount of prism to correct.
I personally hate these bars, I like to use the loose lens prisms,
they're a lot easier to use; my own personal preference.
Certainly with children, you want to use
the loose lenses because they're smaller.
If you use something this big, kid's gonna try to grab it,
it's not gonna work well.
And if you have a tropia that can't be corrected
by correcting with glasses or patching,
then you can always go to surgery;
And basically, when we have eyes out of alignment,
we get them back in alignment,
and we do that by either shortening
or lengthening the rectus muscles.
In this case, this rectus muscle is cut off
from its insertion and it's reinserted
back onto the sclera using suture, and this basically lengthens
the effective length of this muscle and gets things back in alignment.
And you can do the opposite, you can also shorten the muscle
and reattach it back to its original insertion.
Not an easy surgery to do, because you. could imagine,
you're trying to do a scleral pass here
and not perforate into the eye and hit the retina,
and the sclera is very, very thin.
I mean, so thin. We're talking about a third of a millimeter
right underneath this muscle insertion.
You can very easily perforate into the eye,
and not an easy surgery, but very effective.
So that was ocular misalignment. Let's move on.