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103 Cards in this Set
- Front
- Back
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Velocity
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rate of speed at which light travels
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frequency
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number of wavelengths passing a given point in 1 second
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visible spectrum
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400-800 nanometers
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refraction
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bending of light
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If light travels in a straight line, how does one explain this apparent bending of light in water?
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snells law
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emergent ray
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light ray coming from a medium
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incident ray
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light ray entering a medium
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The cost of a lens rises along with its ____
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index of refraction
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Light always bends towards the
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prism base
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Distance between focal point and lens
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focal length
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When you look through a prism objects appear at the
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apex
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2/3 refracting power of the eye
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cornea
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Ideal pupil size is between ___ and ____ mm
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2 & 5
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Axial length is measured from
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anterior cornea to macula
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Refractive error that causes the patient to have trouble seeing clearly at distance
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myopia
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Absolute hyperopia
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hyperopia where amount of deviation cannot be overcome by accommodation, needs lenses
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manifest hyperopia
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max amount of plus power sphere that patient would accept without compromising vision, may be corrected by accommodation or lenses
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With the rule astigmatism
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greatest refractive power in vertical meridian
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anisekonia
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unequal image size
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Stronger the lens _____ the focal length
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shorter
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In myopes ADD is _____ minus
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less minus
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Temple
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arms of glasses
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65mm is average for PD. True or False?
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True
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If patient doesn't look through the optical center of glasses ________ is induced
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prism is induced
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Distometer
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measures vertex distance
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Geneva lens clock measures
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the base curve
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pantoscopic tilt is
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angle in which the frame front angles to the face when the glasses are worn
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eyeglass repair kit includes
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Screwdriver
Screws Nose Pads Grommets |
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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 lines
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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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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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Trifocal power is usually _________ of bifocal power?
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Half ( but sometimes customized for the patient)
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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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Base out prism will represent in ______________
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the temporal section of the circles
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Base up prism will represent in __________
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Upper Circles
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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 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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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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SAPS
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Estimate the spherical component
Refine cylinder axis Refine cylinder power Refine sphere power |
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The cylinder axis of the two eyes usually adds up to
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180 degrees
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What does Push Plus mean
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use the max power of plus powered sphere (or min. minus power sphere) to achieve best VA
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Refractometry
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the measurement of the refractive error of the eye
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Refraction
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done by a licensed professional
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Significant changes in astigmatism over 1-3 year period is likely due to
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refracation error at test
keratoconus chalazion |
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Representation of the dioptic average of the spherocylinder
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circle of least confusion
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How to calculate spherical equivalent
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half the cylinder and combine it with the sphere (use sign of larger number)
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The zero mean power of the crossed cylinder ensure that
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circle of least confusion remains on the retina for both presentations
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Advantage to JCC
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sensitive method for determining cylinder axis and power in both high and low degrees of astigmatism
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Disadvantage to JCC
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patients may have trouble with the sequential presentation of JCC
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In minus cylinder you follow the ______ dot when refining cylinder axis
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red dot
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When refining cylinder power in minus cylinder, if the patient prefers the red dot
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give more minus power
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When refining cylinder power in minus cylinder, if the patient prefers the white dot
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take away power
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How to maintain spherical equivalent, for every 0.50 D change in cylinder power
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you must adjust the sphere by 0.25 D
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Factors affecting refractive errors
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uncontrolled diabetes
increasing nuclear scleroisis pregnancy certain medications (sulfa may induce myopia) |
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Avoid tests that might alter _________ surface prior to refractometry
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Corneal
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Manifest Refractometry
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preformed without drops
people over 40 |
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Cycloplegic Refractometry
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Performed after cycloplegic drops
children/latent hyperopes |
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Duochrome test
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useful for refining spherical power, prevents giving too much minus, fog patient by +0.50D
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Vertex Distance
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distance between the back surface of the lens and front of the eye
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Provides a means of projecting test letters and characters on a screen for the assessment of visual acuity
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acuity projector
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An instrument which has many lens choices to subjectively measure a patient’s refractive error
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Refractor or phoropter
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An instrument which is used to determine the parameters of lenses (power, optical centers, and prism).
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lensmeter
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A caliper used to measure vertex distance.
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distometer
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Placed on a patient’s glasses to allow over refraction with loose lenses.
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Halberg clips (or Janelli)
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Snell’s law
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A comparison of the speed of light in air to the speed of light through a substance.
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Which color has the longest wavelength in the electromagnetic spectrum?
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the color red
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Two prisms placed base to base will create a converging or ______ lens.
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plus lens
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If no lens cleaner is available what is the best way to clean dirty frames and lenses
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With warm soapy water
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What is the recommended height for a bifocal segment in a flat top bifocal?
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At the lower lid margin
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What type of lens would be most suitable for a presbyopic mechanic who must do close work over his head?
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Vocational bifocal
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In general what is the first step in refractometry after the phoropter is aligned?
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Correct as much of the refractive error as possible with sphere.
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A myopic eye has too much ______ power
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too much plus power
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In a myopic eye, where are images of distant objects focused?
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In front of the retina
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An 8 year old complains of not being able to see the board at school. What is the most likely refractive error?
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Myopia (typical presentation is age 8 or 3rd grade)
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transpose Plano -2.00 x 029
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-2.00 +2.00 x 119
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transpose -3.00 -2.50 x 047
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-5.50 + 2.50 x 137
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transpose +2.00 +2.00 x 050
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+4.00 -2.00 x 140
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transpose -8.25 + 0.25 x 180
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-8.00 -0.25 x 090
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transpose Plano +4.50 x 090
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+4.50 -4.50 x 180
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SE of +2.00 -0.50 x 147
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+1.75 sphere
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SE of Plano -4.00 x 063
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-2.00 sphere
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SE of -0.50 -0.50 x 125
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-0.75 sphere
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SE of +1.00 +1.00 x 150
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+1.50 sphere
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SE of -2.50 -2.50 x 048
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-3.75 sphere
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If the thin lines focus at
-1.25 and the thick lines focus at -2.00 and the axis is 180. What is the prescription? |
-1.25 -0.75 x 180
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If the thin lines focus at +2.00 and the thick lines focus at plano with an axis of 090 what is the prescription?
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+2.00 -2.00 x 090
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If the thin lines focus at plano and the thick lines focus at -3.75 with an axis of 025 what is the prescription?
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Plano-3.75 x 025
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The thin lines focus at +2.50 and the thick lines focus at -0.25 with an axis of 045. What is the prescription?
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+2.50-2.75 x 045
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The thin lines focus at +0.75 and the thick lines focus at -1.00 with an axis of 145. The thin lines in the seg focus at +1.75. What is the prescription?
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+0.75 -1.75 x 145
Add +1.00 |
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What is the focal length of a 5 D lens?
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0.2m
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A toric lens is the same as what other type of lens?
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spherocylinder
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