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38 Cards in this Set
- Front
- Back
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Thick lines represent
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cylinder power
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(When working in Minus) If the thin lines come to focus but the thick lines only come to focus when turning the dial towards you, what should you do?
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Change the axis power by 90 degrees, refocus thin lines and try thick lines again.
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If both sets of lines come to focus together then the glasses are...
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Sphere
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Lensometry is
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a procedure used to measure the Rx of a patient's present spectacle lens.
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triple lines are
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cylinder power
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Single lines are
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sphere power
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Which way do you ALWAYS turn the dial when measuring ADD?
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towards you (plus)
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Thin lines represent
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Sphere Power
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If Sphere lines come to focus at 0 then the glasses are...
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plano
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Four principles properties of spectacle lenses
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-Spherical and cylindrical power
-axis -prism -optical centration |
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How is ADD power calculated?
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The difference in its measured power and the spherical portion of the lens.
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ADD is usually between _____D and _____D
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+1.00D and +3.00D
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How do you read progressive or blended ADDs?
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Numbers are etched into the temporal portion of the lenses, can be read with the naked eye or with the PAL ID
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The patient may experience asthenopia if?
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The OCs do not align with the visual axis, inducing a prism.
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What represents a prism in the lensometer?
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The center of the crossed mires
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Trifocal power is usually _________ of bifocal power?
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Half ( but sometimes customized for the patient)
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OC displacement x lens power =
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amount of prism
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Define Reticle.
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a prism scale on which mires are focused and which are marked with a series of circles. Used to center the lens for marking or verification.
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Define Mires.
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Lines projected through the reticle. Three thin lines spaced close together denotes the sphere power and three thick lines spaced farther apart denotes the cylinder power.
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OC of the lens is ....
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Where the two prisms meet.
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Define Axis Drum.
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Large wheel marked from 0 degrees to 180 degrees, used to find the axis location of the lens
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Base out prism will represent in ______________
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the temporal section of the circles
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Often the circles of the reticle are in _____ prism D steps
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1.00
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Base up prism will represent in __________
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Upper Circles
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Define Lens Holder?
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A spring loaded arm that holds the lens securely for reading and marking
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Define Lens Table?
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Adjustable straight metal shelf on which the frame rests and ensures the axis reading is correct
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Define Eyepiece?
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Part of the instrument into which the user looks.
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Define Power Drum
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Large wheel used to find the power of the lens. Marked with power ranging from -20 to +20 D.
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Black numbers represent _____?
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Plus Power
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Base In prism will represent in _________
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nasal section of the cirlces
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What are the two types of lensmeters?
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American crossed-line type target
European dot type target |
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Red Numbers represent ______?
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Minus power
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Base down prism will represent in ___________
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Lower Circles
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The thin lines focus at -0.50 and the thick lines focus at -2.00. The axis is 180. The single lines for seg focus at +1.75.
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-0.50-1.50x180
add+2.25 |
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The thin lines focus at +2.25 and the thick lines focus at -1.75. The axis is 095. The single lines for seg focus at +5.00.
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+2.25-4.00x095
add +2.75 |
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The thin lines focus at +2.50 and the thick lines focus at plano. The axis is 017. The single lines for the seg focus at +4.00.
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+2.50-2.50x017
add 1.50 |
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the denotation of "plano" means that there is no _____ correction.
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no spherical correction (no lens curvature)
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the denotation of "sphere" means that there is no ________ correction.
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no cylinder & axis correction
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