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Using Subjective Refraction to Calculate Glasses Prescription and Fit a Contact Lens

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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
  • 14:26 - 14:31
    the glasses prescription,
    you add 10 degrees and put
  • 14:31 - 14:35
    that in the contact lens if you
    decide to put another one on.
  • 14:35 - 14:38
    That rule is commonly
    referred to as the Lars rule.
  • 14:38 - 14:40
    So, if it's to
    the left, you add.
  • 14:40 - 14:42
    If it's to the
    right, you subtract.
  • 14:42 - 14:45
    So, in this case, it was
    to the left ten degrees,
  • 14:45 - 14:48
    so we added ten degrees to
    the glasses prescription,
  • 14:48 - 14:52
    and then we place that on
    the contact we use that
  • 14:52 - 14:54
    in the final contact
    lens prescription.
  • 14:55 - 14:58
    Now, after the contact lens
    has settled, then you check
  • 14:58 - 15:01
    the visual acuity, and then
    you will do what's commonly
  • 15:01 - 15:03
    called an overrefraction.
  • 15:03 - 15:05
    Now, an overrefraction
    is to make sure that
  • 15:05 - 15:08
    the contact lens is not too
    weak or too strong,
  • 15:08 - 15:10
    or that you've got
    the axis wrong.
  • 15:11 - 15:15
    And for soft contact lenses,
    most of the time, as long as
  • 15:15 - 15:17
    you vertexed correctly,
    put the correct contact
  • 15:17 - 15:21
    lens on, the overrefraction
    should be close to plano.
  • 15:21 - 15:24
    But behind the phoropter,
    it's always good to make sure,
  • 15:24 - 15:27
    so you do a spherical refinement
    to make sure the patient is not
  • 15:27 - 15:30
    accepting more plus or more
    minus, or in some cases,
  • 15:30 - 15:31
    some astigmatism.
  • 15:32 - 15:34
    Thank you for
    watching this video.
  • 15:34 - 15:38
    Again, I'm Dr. David Meyer,
    and today's video was about
  • 15:38 - 15:41
    fitting a patient with a soft
    contact lens after doing
  • 15:41 - 15:43
    a basic subjective refraction.
  • 15:44 - 15:45
    Thank you.
Title:
Using Subjective Refraction to Calculate Glasses Prescription and Fit a Contact Lens
Description:

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Video Language:
English
Duration:
15:46

English subtitles

Incomplete

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