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15 Cards in this Set
- Front
- Back
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What is the purpose of the clock dial?
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To get a gross estimate of the astigmatic correction (in other words, a tentative axis and power)
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What will the clock dial look like if there is no astigmatic error?
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All spokes will look alike (fuzzy). No one spoke will stick will be more distinct.
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Assuming the CLC is on the retina, which focal line will appear the clearest.
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-the line closest to the retina
-if the patient is fogged, the most posterior line will be the clearest |
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Assuming the patient is fogged, which focal line will move with the addition of minus lenses?
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- the anterior focal line
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What happens to the interval of sturm when cylinder lenses are added?
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-the I/S is decreased
-the focal lines move closer -the focal lines become smaller (shorter) |
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What happens to the focal lines when too much cylinder is added?
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The interval of Sturm flips (what was clear vertical lines are now clear horizontal lines)
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Describe the set up for the clock dial.
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-occlude the non tested eye and remove all cylinder lenses from the phoropter
-fog the patient (if after ret., don't take out your working distance) -NO first best sphere, because you want the patient fogged -confirm that all lines are equally blurred |
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Describe the method.
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-while decreasing plus, ask the patient to tell you when one or some of the lines appear clearer than others
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What do you set the axis to on the phoropter?
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Multiply their answer by 30, this is the AXIS.
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Why do you make sure that the lines on either side of the axis are equally dark?
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you want the lines on either side of the axis to be equally dark. If one side is darker, then you need to shift the axis away from that side.
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How do you know that you added enough cylinder lenses?
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When all lines appear equally dark. If you add too much, the opposite line becomes darker and clearer.
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Why would the clock dial fail?
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-fogged too much
-not enough fog to stablize accommodation -patient accommodative instability -uncooperative or unresponsive patient -cylinder too high for patient to respond |
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How do you perform the clock dial using a plus cylinder phoropter?
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-set the axis opposite to what they say
-adding plus cyl. will move the posterior focal line -this will make it foggy, therefore, you must add minus SPHERE to compensate |
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Can you perform the clock dial on an absolute presbyope who is overminused?
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-Yes, add minus cyl, with plus sphere clicked in
(can not be done with a plus cylinder phoropter) |
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What are the intervals between lines for the clock dial and the Lancaster-Regan (sunburst)?
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clock dial=30
Lancaster-Regan=10 |
