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[DR. DAVID MEYER] I'm
Dr. David Meyer.
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I'm the director of Contact Lens
Services here
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at the Moran Eye Center
in Salt Lake City, Utah,
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and today we're gonna go through
how to calculate a glasses
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prescription for a patient,
and then based on that,
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how to properly fit
a contact lens to that patient.
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One thing that's very important
to remember when your patient
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comes in is case history.
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Find out the last eye exam,
any medical issues in general,
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any previous history of eye
surgeries or eye diseases
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or any complications that
they may have had in the past.
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To begin the exam
will start with calculating
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a glasses prescription.
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We're gonna start by
putting the phoropter
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in front of the patient,
and what's really important
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is, first of all, to make
sure that the pupil distance
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in the phoropter matches the
pupil distance of the patient.
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And in order to do that,
there's this knob here
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at the top that adjusts
whether the pupil distance
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is smaller or larger.
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In this case,
this patient has
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a pupil distance of 62,
and so I'm gonna set it up here
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at this indicator line at 62.
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Another important thing
to factor in is to make sure
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that the phoropter
is level, and to do so,
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you use this leveling window
here, and to adjust it,
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you turn this dial above,
and you try to get it
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so it's just level right there.
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So the bubble and dot match up.
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Now, in this case,
we're gonna start
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with the right eye and then
go to the left eye.
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In order to do so,
you turn this knob
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so it reads OC.
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That means to
occlude the left eye.
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So currently, both of his eyes
are open, but he can only see
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through his right eye because
the left eye's occluded.
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Now, to begin this,
I'm going to blur the patient
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so that the
letters there are very blurry,
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and because
of previous readings,
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I already have an idea of
roughly what the prescription
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is based on his last glasses.
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But I'm gonna start out by
making his vision very blurry
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in the right eye, and I'm gonna
explain to the patient
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to tell me as soon as
he can read these letters
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even if they're blurry, but
as soon as he can read them.
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Right now,
I have displayed the 20/30 line.
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The 20/30 line is a good line to
begin refining your refraction.
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So in this case,
I want you to tell me
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as soon as you can start
to read those letters,
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even if they're blurry.
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And I'm slowly adding more
minus to his prescription.
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Right now.
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About there.
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So right when they say,
'About there,' you know
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that you need to add another
0.5 to 0.75 more minus,
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and that's gonna be in the
ballpark of your prescription.
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So in this case, I'm continuing
to refine the sphere.
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So the sphere is on this
side of the phoropter,
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and I'm refining it to get
as close as we can before
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I start refining the cylinder
component of his prescription.
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So I'm gonna ask him,
'Is this any better?'
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[STUDENT] Yes.
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[DR. DAVID MEYER] And
even better?
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[STUDENT] Yes.
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[DR. DAVID MEYER] And at this
point, once you get a good
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ballpark of the spherical
component of the prescription.
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Now you switch over to
do the cylinder portion
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of his prescription.
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And to do so, I turn this.
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This lens is called the JCC.
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The JCC is short for
Jackson Cross Cylinder,
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and it helps us refine
how much astigmatism
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he has and what the orientation
of that astigmatism is.
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And in this case,
as I flip it, as you can tell,
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I'm gonna be asking him what
looks more sharp and clear.
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So in this case,
I'm gonna ask him
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what is more sharp and clear,
Number 1 or Number 2?
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[STUDENT] Number 1.
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[DR. DAVID MEYER] So in
this case, he said Number 1.
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And for a plus cylinder
phoropter, which this is,
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we turn the dial in the
direction of the white dot
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here on the JCC.
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So in his case,
because he said Number 1
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is better, I turn the dial.
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Currently, it's at
about 85 degrees.
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I turn it to about 75 in this
case, and then I ask him again.
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And let me reiterate here
that right now in the JCC,
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the two dots are straddling
this axis here.
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So right here on this axis
refinement, where all these
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numbers are zero through 180,
the line right now matches up
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at axis 75, and these two
dots are on either side of that.
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So that's important in order
to figure out where the axis
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of his prescription is.
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So in this case,
I'm gonna move it here,
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and I'm gonna say,
'What's more clear,
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Number 1 or Number 2?'
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We'll do it again.
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Number 1 or Number 2?"
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[STUDENT] Number 2.
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[DR. DAVID MEYER] Okay, good.
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So I'm gonna move it toward
the direction of the white,
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which is this way.
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I'm gonna ask him again,
'Which is more clear,
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Number 1 or Number 2?'
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[STUDENT] They're
about the same.
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[DR. DAVID MEYER] Pretty close.
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Just to be safe,
I'm gonna move it
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a little bit more in that
same direction and ask him again
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what's more sharp and
clear, Number 1 or Number 2?
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[STUDENT] Number 1.
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[DR. DAVID MEYER] Number 1.
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So we're gonna go back
to where we began here,
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which is at axis 55,
and based on his previous
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glasses that he walked in
with, or previous refraction,
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or whatever previous
prescription we have,
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we know that that's pretty
close to what he had before,
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so we know we're on
the right track.
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Now, in order to refine how
much cylinder he needs in his
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prescription, we have to turn
the JCC so now the dots
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line up with this
little arrow here.
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So right now,
the two white dots here
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match up at axis 55 that
you can see there,
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and that is how you begin
your power refinements.
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And so in this case,
it's the same thing.
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If he likes it when
the white is lined up,
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that means you want to
add more cylinder.
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If he likes it when the red
is lined up, he wants less.
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So in this case,
let's ask him.
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What's more sharp and clear,
Number 1 or Number 2?
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[STUDENT] Can
I see them again?
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[DR. DAVID MEYER] Yeah,
Number 1 or Number 2?
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[STUDENT] Two.
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[DR. DAVID MEYER] Two, so
he liked it better with the red,
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and currently,
he has one diopter
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of cylinder in there,
so I'm gonna take out
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a quarter, and then I'm gonna
ask him again
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what's more
clear, Number 1 or Number 2?
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[STUDENT] About the same.
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[DR. DAVID MEYER] Pretty close.
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And I wanna be a
little more sure,
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so I'm gonna take it
down to 0.5 cylinder,
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and because I've added 0.5
cylinder of essentially minus,
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because I'm taking away some
plus, to compensate for that
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I have to add a quarter of
plus here in the spherical
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component of the phoropter
to maintain
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a spherical equivalent
of the prescription.
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So we'll ask him again,
what's more clear,
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Number 1 or Number 2?
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[STUDENT] About the same.
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[DR. DAVID MEYER] About
the same.
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So in this case,
since it's about the same,
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you know that you're very
close to what we need.
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Just to check one more time,
I'm gonna bring this down to
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0.25 cylinder and ask him again,
Number 1 or Number 2?
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[STUDENT] Definitely
Number 1.
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[DR. DAVID MEYER] Definitely
Number 1.
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And we'll do one more time,
what do you like better?
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This is Number 1 or Number 2?
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[STUDENT] They're
still pretty close.
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[DR. DAVID MEYER] They're
still pretty close.
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So at that point,
we've now refined
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the axis of the cylinder,
and now we've refined the degree
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or the power of the cylinder.
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So as you can tell
here, right now,
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it's a negative 575
plus 50, axis 45.
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And then to go back,
I'm gonna go back
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to the spherical component
and refine that a little bit.
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I'm gonna ask him
a few more questions.
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What looks more sharp and
clear, Number 1 or Number 2.
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[STUDENT] Two.
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[DR. DAVID MEYER]
Number 1 or Number 2?
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[STUDENT] One.
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[DR. DAVID MEYER] One.
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Now, there are other means
by which you can make sure
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that you haven't overminused
or overplused the patient.
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You can balance the eyes if
we're working on both eyes
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and that's something we can
cover in a different segment.
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But for now,
based on his
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previous findings,
his last glasses prescription
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and what we
found on an autorefractor,
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for example,
we know we're pretty darn close,
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and then you're gonna have the
patient read those letters.
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[STUDENT] O, F, L, C, T.
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[DR. DAVID MEYER] Okay.
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And we can even make it
down to the 20/20 line.
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Go ahead and read that.
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[STUDENT] T, Z, V, E, C, L.
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[DR. DAVID MEYER] Excellent.
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So now that we've got
the glasses prescription
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calculated, at that point,
we need to work on fitting
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the patient with a contact lens.
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Now, when the patient expresses
desire to wear a contact lens,
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there are a number of factors
that you need to consider.
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You need to consider how
much the patient wants to
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wear the contact lens.
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Every day or once in a while.
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You need to find out about
past history of his eyes.
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Does he have dry eye problems?
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Does he have keratoconus or
another corneal abnormality?
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Those are all very important
questions to ask to help
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fit the lifestyle
of the patient.
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For today's purposes,
we're gonna be fitting
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the patient with a monthly lens.
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This particular one is
called a Biofinity Toric.
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It's a lens where you take it
out at night and put it in
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the morning, and after
one month, you throw it away.
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But we're gonna go
through and show
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how to put it on a patient's
eyes, how to assess it,
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and how to get the best
vision out of it.
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Now, one thing that's very
important is when you calculate
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a glasses prescription,
remember that that is
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almost always different than
a contact lens prescription.
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The reason why is because the
optical surface of glasses
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sits out, on average,
about 12 millimeters from
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the front surface of an eye,
whereas a contact lens rests
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directly on the eye.
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So, that changes the optics,
so be sure you use
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a vertex calculator to determine
the correct prescription
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for a contact lens.
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For example, for this patient,
the spherical equivalent of his
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prescription is a negative 5.75.
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If you put that in a vertex
calculator what that would give
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you is that the proper contact
lens would be a negative 5.5.
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Now, in today's purposes,
we're gonna put a toric
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contact lens on his eye for
demonstration purposes only.
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And before we do that,
it's very important that you
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get some keratometry reading,
whether manual keratometry,
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automated, or even a topography.
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Any of those will help
determine which base curve
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and diameter would be best
suited for the patient.
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So, for today's purposes, like
I said, we're gonna be fitting,
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fitting the patient with a
Biofinity Toric contact lens,
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and when you take it out
of the blister pack,
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it's important to make sure
that the contact lens
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is not inside out.
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And the best way to tell is to
hold it up against the light,
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and if you look at the edge
of the contact lens,
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the edges should point
straight up toward the
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ceiling like a bowl.
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If you look at it,
and the edges are kind of
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flared out or splayed out
or they're flattened out,
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that usually means
it's inside out.
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Now, that usually doesn't
cause a lot of problems,
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but it can cause some
discomfort for the patient,
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so make sure that the contact
lens is not inside out.
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Now, I've put the contact lens
on the edge of my finger, and
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contact lenses typically stick
to the surface that is wetter.
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And so try to make sure that
your finger is nice and dry
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so that the contact lens
will stick on the patient's eye
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instead of your finger.
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Now, to do so,
I'm gonna have
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the patient lean back
and look up high
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toward the ceiling,
and very gently,
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I'm gonna pull down on
the lower lid
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and pull up on the upper lid.
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And as he looks up high,
I'm gonna first place it on,
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close to the lower limbus
of his cornea, like so.
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Now, have the patient look
down toward the floor,
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because when you look
down toward the floor,
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it has a tendency to help
center the contact lens.
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And make sure that the patient
blinks normally
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to help center the contact
lens even more.
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Now, when you place the contact
lens on the patient's eye,
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be sure to give the contact
lens a couple of minutes
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to settle down, especially
if it's a toric lens.
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A toric lens has a tendency to
orient in the correct position,
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but it takes a few minutes for
the patient's natural blinks
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to put it in the
correct position.
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In this case,
we've given the patient
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a good solid
five minutes
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to let the contact lens
settle down.
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At this point,
I'm gonna pull
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the slit lamp over here
and take a close-up look
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at the lens to make sure
it's fitting properly.
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Come on forward, put your
chin down there,
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and your forehead
resting forward.
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Now, there are several factors
when assessing a contact lens.
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Number 1, what we can do
is we can pull down on
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the lower lid just gently, and
we can see the toric marking.
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In this particular
brand of contact lens,
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the toric marking should
be ideally at 6 o'clock.
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As you can see here,
the contact lens is about
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ten degrees to the left,
so it's rotating
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a little bit temporally.
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As you assess this,
have the patient blink
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normally, and as he blinks,
you can see the movement
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of the contact lens.
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Now, ideally,
you would like
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the contact lens to
move a little bit,
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maybe 0.1 to 0.2
millimeters, but not too much,
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because if it's too much,
then it'll be uncomfortable.
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Blink.
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Another important thing is to
make sure there's full limbal
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coverage and that the contact
lens extends beyond the limbus
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onto the conjunctiva, and it's
not rubbing against the limbus.
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In this case,
the contact lens
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is rotating about
ten degrees temporal,
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or as you're looking
at his right eye,
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it's rotating to my left.
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In that case,
whatever the axis of
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the glasses prescription,
you add 10 degrees and put
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that in the contact lens if you
decide to put another one on.
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That rule is commonly
referred to as the Lars rule.
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So, if it's to
the left, you add.
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If it's to the
right, you subtract.
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So, in this case, it was
to the left ten degrees,
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so we added ten degrees to
the glasses prescription,
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and then we place that on
the contact we use that
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in the final contact
lens prescription.
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Now, after the contact lens
has settled, then you check
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the visual acuity, and then
you will do what's commonly
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called an overrefraction.
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Now, an overrefraction
is to make sure that
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the contact lens is not too
weak or too strong,
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or that you've got
the axis wrong.
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And for soft contact lenses,
most of the time, as long as
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you vertexed correctly,
put the correct contact
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lens on, the overrefraction
should be close to plano.
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But behind the phoropter,
it's always good to make sure,
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so you do a spherical refinement
to make sure the patient is not
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accepting more plus or more
minus, or in some cases,
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some astigmatism.
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Thank you for
watching this video.
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Again, I'm Dr. David Meyer,
and today's video was about
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fitting a patient with a soft
contact lens after doing
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a basic subjective refraction.
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Thank you.