Term
| What is the definition of Glass |
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Definition
| Amorphous, supercooled liquid with high viscosity. Random molecular structure |
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Term
| What are the basic ingredients of glass |
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Definition
| Silica, sodium carbonate, and calcium oxide |
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Term
| What is added to make ophthalmic crown glass? |
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Definition
| Trace amounts of potassium, borax, antimony, and arsenic |
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Term
| What is added to make flint glass? |
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Definition
| Lead oxide. Increases refractive index but also increases dispersion. |
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Term
| What is used to make barium crown glass? |
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Definition
| Uses barium oxide. Increases refractive index with less dispersion than flint glass. |
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Term
| What is used to make high index glasses? |
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Definition
| n > 1.6 uses varying amounts of titanium oxide |
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Term
| What is added to colored lenses? |
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Definition
Blue = cobalt
Green = chromium oxide
Violet = magnesium
Yellow = uranium |
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Term
| What is used in non-visible radiation absorption? |
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Definition
Ultraviolet = cerium oxide
Infrared = iron oxide |
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Term
| What is used to make photochromic glass? |
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Definition
| Silver halide crystals to vary lens transmission. |
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Term
| What are plastics made up of? |
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Definition
| Cellulose, casein, oil, coal, or natural gas |
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Term
| What are the two main groups of plastic |
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Definition
| Thermoplastic and thermoset |
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Term
| What are common thermoplastic materials? |
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Definition
| acrylates (plexiglas), polycarbonate |
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Term
| What are the numbers for CR-39 lenses |
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Definition
n = 1.586
Abbe # = 58
Specific Gravity = 1.32 |
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Term
| What are the numbers for polycarbonate? |
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Definition
n = 1.586
Abbe = 30
Specific Gravity = 1.20 |
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Term
| What are the numbers for ophthalmic crown glass? |
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Definition
n = 1.523
Abbe = 58.9
Specific Gravity = 2.54 |
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Term
| When you get to an abbe number of _____ or less there will be significant chromatic aberration. |
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Definition
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Term
| What plastics/synthetics are used for frames? |
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Definition
Zyl - no longer used but has stuck as a nickname
Optyl (epoxy resin)-not used as much currently
Carbon Fiber, polyamide, and kevlar |
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Term
| What metals are used for frames? |
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Definition
Nickel silver (copper, nickel, and zinc) - allergic
Titanium - expensive
Stanless steel |
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Term
| What are nosepads made of? |
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Definition
| silicone or cellulose acetate (plastic) |
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Term
| What measurement is called the eye size? |
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Definition
| A or horizontal measurement |
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Term
| What is the geometric center of a lens? |
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Definition
| The center of midpoints from the A and B dimensions, the physical center of the lens. Has nothing to do with optics. |
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Term
| What is the mechanical center of a lens? |
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Definition
| The point that the lens rotates about during the edging process. |
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Term
| What is the ED (effective diameter)? |
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Definition
| Two times the longest distance from the GC to the eyewire. |
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Term
| How is MBS (minimum blank size) calculated? |
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Definition
| MBS = ED + 2(decentration) |
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Term
| What is the MRP (major reference point)? |
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Definition
| The point on the lens that has the prismatic effect that is called for in the prescription |
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Term
| What is the distance reference point |
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Definition
| The point on the lens, as specified by the manufacturer, at which the distance sphere power, cylinder power, and axis position must be measured |
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Term
| What is the near reference point? |
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Definition
| The point on the lens, as specified by the manufacturer, at which the power of the add is measured |
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Term
| What is the fitting point? |
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Definition
| The point on the lens, as specified by the manufacturer, which is used as a reference point for positioning the lens in front of the wearer's eye. |
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Term
| What is the prism reference point? |
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Definition
| The point on the lens, as specified by the manufacturer, at which the prism value of the finished lens is to be measured. In non-aspherical single vision and standard multifocal lenses, the prism reference point and the fitting point are the same. |
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Term
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Definition
| A system for generating an image at the second focal point of the lens under test. Comprises an axially adjustable target, a collimating lens, and a rest to hold the test lens. The lens rest coincides with the second focal point of the standard lens. Measures the back vertex power of the test lens. |
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