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23 Cards in this Set
- Front
- Back
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What is the thinnest a SV Plus lens can be? |
1.9mm at thinnest point
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What is the thinnest minus a single vision lens can be? |
2.0 mm at the thinnest point what is the tolerance of a sphere |
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What is the tolerance of a sphere power over 6.50? |
+/- 2% |
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2 types of Aphakic lenses |
Aspheric - emulates the shape of the eye: steeper curve in the center, flatter towards the periphery
Lenticular - high plus rx to minimize lens thiskness
Can be spherical or aspheric |
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What is the tolerance of the multifocal adds |
+/- 12 D |
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Occupational Lenses |
Prescribed for specialized occupational or recreational needs |
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What is the tolerance of a cylinder power above 4.50? |
+/- 4% |
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What is the tolerance for horizontal prism? |
.66 Or MRPs within 25 mm |
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What is the tolerance of seg height? |
+/- 1.00 mm |
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What is the tolerance of axis power 0.875 to 1.599 |
+/- 3 degrees |
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Progressive Bifocal |
No transition line, no image jump Usable intermediate area Cosmetic advantages Distortion at corners may be hard to adapt to Intermediate area relatively small |
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Trifocal |
Intermediate zone and bifocal Ex: 7x28 7= mm deep (intermediate) 28= bifocal top
Intermediate = 50% of bifocal add |
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What is an Aphakic lens and what is it used for? |
A post cataract surgery lens |
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Slab off |
Biocentric grinding- base up prism ground into the reading portion of a lens to minimize the excessive vertical prism imbalance |
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Crown Glass |
1.533 index of refraction 2.55 Specific gravity 59. V value
Less dispersion, impact resistant when Chem/heat treated, scratch resistance- good |
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Photochromatic Glass |
Silver halide crystals in glass lens that respond to UV wave 300-400 mm "exposure memory" |
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Polarized lenses |
Contains a filter ofnpolyvinyl alcohol "sandwiched" between glass or plastic lens material
Admits light vibrating only on vertical plane
Reduced glare off reflected surfaces (water, snow, metal) |
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Tolerance is sphere powered lens of 0.00 to 6.50 |
+/- 13 D |
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Standard index of refraction |
1.530 |
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Compound lens |
Combination of a spheric lens with a cylinder |
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Index of refraction of polycarbonate lens |
1.586 |
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Index of refraction of hi index lens |
1.67 and 1.74 |
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Index of refraction of Crown Glass |
1.532 |
