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61 Cards in this Set
- Front
- Back
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CR-39 is available in which widths
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25, 28, 35, 45
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Where is the SOC of the FT located in all except the FT 45
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5 mm below the segment top
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What is the segment depth for FT
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the full visible vertical measurement of the segment.
equal to one half the segment width plus the distance from the SOC to segment top |
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What powers are FTs available in
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+0.75 to +6.00
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The RT is available in which add powers
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+0.75 to +30.00
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Round segment adds are available in which sizes
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22, 24, 25, 28
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What is the segment depth for the round seg?
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the diameter of the segment button
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Where is the SOC of the round seg located
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At the center of the circle. and the seg is paced on the front side of the lens
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Where is the SOC of the executive lens
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at the segment top with the segment on the front side of the lens (no image jump)
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What is the seg width and depth for an ultex lens (2)
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seg width: 38 and 40 mm. seg depth: 19mm and 33mm respectively.
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What material does ribbon come in
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glass
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When measuring prism with the lensometer, why is the target always displaced in the direction of the prism base?
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because the telescopic system of the lensometer inverts the image, which causes the image of the target to be displaced towards the base instead the apex.
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What is the "resultant optical center"?
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It is the place on the lens where prism from the carrier lens and segment combine to equal zero prism. It is found within the segment, where the target is centered in the reticule.
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What is the easier way to distinguish CR-39 bifocal from a glass bifocal
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The CR-39 bifocal will have a ledge from its one-piece concept whereas the glass bifocal will not. The glass bifocal is fused.
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Why is it important not to move the lensometer stage height when going from one lens neutralization to the other lens?
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So that you will not miss accurately measuring vertical prism if the target is not vertically centered when moving to the other lens
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On a progressive lens, where is prism verified?
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On the distance O.C. (the dot below the fitting cross)
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When edging a finished SV lens, what is the sequence of steps to take?
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1. MBS determination.
2. Layout 3. Blocking 4. Edging 5. Safety bevel 6. Glazing |
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What is a non-selective absorbing lens and give an example of a glass non-selective absorber
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A non-selective lens reduces the transmittance without altering the proportions of the various wavelengths. an example is the grey tint glass lens
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To reduce surface reflection, what are the two conditions that the ARC coating must have with respect to the lens substrate?
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Amplitude condition--> coating's n must equal to the square root of the substrate's n
Phase condition--> coating's thickness is 1/4 the wavelength of light |
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How does one easily identify if an absorptive glass lens is proceeded by surface color coat or the oxide is in the glass melt
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a. If the glass has surface color coat, the tint will be uniform regardless of prescription
b. Glass with oxide in it has color that is dependent on the thickness (thus prescription) or the lens. With a plus lens, it will be darker in the middle. With a minus lens, it will be darker at the edges. |
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What are the two advantages of glass photochromics over plastic photochromics other than being more scratch resistance?
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a. glass photochromics become darker than plastic in UV light.
b. Glass photochromics don't fatigue like in plastic. Fatigue is when the photochromic molecules no longer function as efficient as before. |
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When is the approximate method of neutralizing a multifocal lens the same as the exact method?
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Approximate and exact methods are the same when neutralizing a minus lens or a plus lens less than +3.00 D. It is also the same if the add is on the concave side
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From which side of a the frame should a lens be glazed and why?
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Should be from the front of the frame, on the temporal side because if the frame is impacted, the lens will tend to pop out from the front side (where it was inserted) and will less likely cause damage to the wearer
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How does add power measured by the exact method compare with a measurement by the approximate method (for plus vs. minus powers)? Identify direction of power change
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a. The approximate is usually greater than exact by about +0.50 for a high plus carrier lens (> +3.00 D)
b. For a minus carrier lens, there is no difference between approximate and exact method add powers |
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Give two reasons why a safety bevel is placed on lenses
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a. So the lens doesn't chip while inserting it into the eyewire
b. So the edges are smoothed out so they don't cut the patient's cheek |
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during the blocking of lenses for edging, a plate with fine vertical lines is moved with respect to a solid non-movable line on the blocking unit. What do the positions of the fixed non-moveable line and movable line represent?
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a. The fixed non-movable line represents the G.C.
b. The movable line represents the O.C. (the amount of decentration for the IPD) |
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What is the optimal pantoscopic tilt, vertex distance, and frame B dimension when fitting PAL's
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Pantoscopic tilt: 12 degrees
Vertex distance: no longer than 14 mm B dimension: 38 mm |
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When tinting CR-39 lenses, is it possible to make a lens already one color and immerse it into another tint?
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Yes, there is a neutralizing tint that will clean (bleach out) the existing color. Once that is cleaned, you will dip the lens into a new color
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Do plastic photochromics and glass photochromics both have temperature dependent issues?
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Yes, both get darker in cooler temperatures
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Does the quantity of metallic oxide in a glass absorptive lens affect its transmission?
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The more metallic oxide, the darker the lens. A darker lens will absorb more UV light, so less UV light is transmitted. The quantity of metallic oxide does no significantly affect the amount of visible spectrum transmission
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Can a scratch resistant coating be applied after a lens has been edged by the manufacturer?
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Yes, but it is better to have SRC directly put on the manufacturers
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What is the segment width of a "golfer classic"?
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15 mm round top
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Why is the near mono PD not required for PAL's?
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The PAL's are made with a specific corridor/near segment width and length that is inset according to standard measurements automatically. Therefore, they do not require a near PD, only distance monocular PD's are required.
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What is the significance of a hydrophobic coating?
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the hydrophobic coating is placed over the ARC. It is used to protect the lens and the coating and to minimize some of the problems with ARC.
ARC problems: water spots, oily or greasy appearance, and an affinity for dust |
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Identify the factors that affect the performance outcomes of glass photochromic lenses? (4)
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Temperature, Illumination, Lens thickness, Tempering method
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Describe the clinical procedure for determining the amount of prismatic effect (if any) that a patient may be experiencing or viewing through their glasses
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a. measure patient's pd
b. neutralize their glasses and dot the OC and measure frame PD c. Calculate the decentration if PD and OC are not equal d. The amount of decentration can be converted to prism power by Prentice's rule e. Or, use patient's PD as PRP and use lensometer to determine if there's prismatic effect |
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You are neutralizing a bifocal lens and the segment button is positioned over the lens stop such that the target is centered on the reticule. What is this point on the lens known as?
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Resultant OC
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What is the major disadvantage to glass through-and-through absorptive lenses (made with metallic oxide in glass melt)?
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color is darker in the center with convex lenses ("target" effect) and darker at the edges ("raccoon" effect) with concave lenses
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What is the "textbook" segment height recommendation when measuring for a first time: FT bifocal wearer, FT trifocal wearer, PAL wearer
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FT Bifocal wearer: at the lower lid margin
FT trifocal wearer: at the lower limbus or lower pupillary margin PAL wearer: in the center of the pupil |
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What is the approximate temperature of the plastic dye bath when tinting CR-39
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200 degrees Farenheit
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How can you differentiate a color tinted glass lens from a color coated glass lens?
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best differentiated by the ARC-like appearance on a color coated lens
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When using the progressive addition lenses in the MDS, what does the white line on the lens represent?
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the fitting cross or where the center of the pupil should be in the frame.
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What is the difference between the surfacing and finishing phase in prescription lens fabrication?
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surfacing is performed on a semifinished lens blank. The lens is layed out, blocked, and then surfaced for the proper Rx. This makes a finished lens blank.
Finishing phase is performed on a finished lens blank. THe lens is layed out, blocked, edged, and then is ready to be inserted into the frame. The finishing phase but not the surfacing phase involves edging. Surfacing but not finishing involves grinding one surface for the final Rx. |
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What is the rederite occupational segment lens
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minus add multifocal
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What is the segment separation for the Double D/R/E?
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13mm
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What are the four parts of a PAL?
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1. Major (distance) lens
2. Transition corridor 3. Near portion 4. Peripheral portion |
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Which dimensions are needed for PALs
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1. measurement from pupil center to bottom of eyewire should be at least 22.0 mm
or... B dimension should be at least 38.0 mm 2. ideal 12 degree pantoscopic adjustment and have adjustable end pieces and nosepads 3. Frames should have no more than 12-14 mm vertex distance |
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What information is needed in a multifocal lab form? (7)
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1. add power
2. segment style 3. segment height 4. near IPD 5. SVL requirements 6. distance IPD 7. frame info |
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What is distance, segment, and total decentration?
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distance decentration: distance between frame GC and lens OC
segment decentration: distance from major lens OC to segment OC in MF lens Total decentration: distance from frame GC to segment center |
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What info do SVL need for fabrication?
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Rx, DIPD, frame info
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What are the major steps to lens finishing? (6)
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1. Proper lens blank selection
2. Layout and blocking 3. Edging 4. Safety Beveling 5. Lens Insertion 6. Final Inspection |
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What is the proper lens blank selection?
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MBS=ED+2(dec per lens)
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What is the edger setting?
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1. measure horizontal dimensions of pattern with box-o-graph device
2. subtract 36.5 3. subtract net result from boxed A dimension 4. Err on the larger size |
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What is "Hide-a-Bevel"?
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all of the thickness is seen from the back side of the frame and the front edge is flush with the frame front
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What is "1/3-2/3 Bevel"?
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peak is shifted, 1/3 of lens thickness is forward of peak, 2/3 behind peak
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What is a safety bevel?
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the concave and convex edge of the lens should be smoothed out, to prevent chipping during lens insertion
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The absorption of the medium may be increased by which 3 methods?
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1. metallic oxides in glass, which decrease transmission
2. colored vacuum coatings (glass) 3. Tinting or coating the lens to achieve a desired absorbance (plastic) |
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Tints can be prescribed for what reasons (4)
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comfort, cosmesis, safety, occupational.
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Rate of density change in photochromic lenses is a function of what 3 things?
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age
lens tempering method ambient temperature |
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What multifocal lens type will give the same ADD power if measured by the exact or approximate method?
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Ultex A bifocal--a MF with the segment on the back of the lens
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What are two advantages of glass photochromics over plastic photochromics other than scratch resistance
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can withstand higher temperatures
can absorb UV wavelengths more efficiently with the AgCl crystals |
