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87 Cards in this Set
- Front
- Back
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The study of lens materials, types, and forms, and how they affect the performance of an ophthalmic lens is...
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Ophthalmic Optics
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The art and science of prescribing, fitting, and adjusting, or otherwise modifying spectacles and related devices for the correction of ametropias and other disorders of the visual system is...
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Ophthalmic Dispensing.
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When does opthalmic dispensing begin and end?
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Begins with case history.
Ends when the patient picks up specs |
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What are the 3 criteria for acceptability of a pair of specs?
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1. Visual comfort
2. Physical comfort 3. Visual demands met |
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What are the three roles of specs in optometry?
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1. The main reason people visit ODs
2. The major therapeutic device Rxed 3. The major source of income for ODs |
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Which helium line defines the index of refraction of a material? What is its wavelength?
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Yellow helium line, d
587.56 nm |
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Does a higher index of refraction allows a lens to be thinner or thicker?
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thinner
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What is the longitudinal chromatic aberration of an optical material called?
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Dispersion
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What greek letter is used to define dispersion?
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omega
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What are the wavelengths for the red and blue helium lines?
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red, C: 656.27
blue, F: 486.13 |
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What is the name for the reciprocal of the dispersion?
What symbol represents it? |
The Abbe number
V |
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V=1/omega
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Abbe Number
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Does a higher Abbe number mean more or less dispersion?
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Less
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What is defined as the ratio of the weight of a given volume of material to the weight of water with the same volume.
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Specific gravity
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What does specific gravity depend on?
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The density of the material
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Does a higher specific gravity indicate a heavier or a lighter material?
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Heavier
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Three descriptors of glass
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1. Amorphous
2. Supercooled liquid 3. High viscosity |
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Is glass crystalline?
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No
It's uniform in composition Its random in molecular structure |
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What are the basic ingredients of glass?
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silica (from quartz sand)
sodium carbonate calcium oxide |
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What is different in flint glass?
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lead oxide
-increases refractive index -increases dispersion |
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What is different about barium crown glass?
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barium oxide
- increases refractive index -less dispersion than flint glass |
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What is different about high index glass?
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titanium oxide
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What is different about absorptive glass?
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Use different metal oxides in varying combos
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What is different about absorptive lenses that absorb non-visible radiation?
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Use cerium oxide for UV
Use iron oxide for infrared |
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What is different about photochromic glass?
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Use silver halide crystals
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What are the two ways that the impact resistance or strength of a glass lens can be improved?
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1. Heat tempering
2. Chemical tempering |
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Which type of glass is "optically superior and more stable?"
What are the downsides of this glass type? |
Crown glass
Thicker and heavier lenses because of low refractive index and high specific gravity. |
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What are 2 descriptors of plastic?
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1. polymeric (organic) material
2. large molecular weight |
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Plastics are often synthetic materials combining what two types of materials?
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organic and inorganic
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What are some common organic materials used to make plastic?
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cellulose
casein oil coal natural gas |
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What are some common types of inorganic materials used to make plastic?
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carbon
hydrogen oxygen nitrogen chlorine sulfur |
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What are the 2 main groups of plastics?
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Thermoplastic materials
Thermosetting materials |
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Which type of plastic will soften when heated and can be stretched, pressed, or molded without changing their chemical structures?
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Thermoplastic materials
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What are some common thermoplastic materials?
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Plexiglas
PMMA Polycarbonate Nylons Vinyls Polystyrene Cellulose acetate Cellulose nitrate |
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Which type of plastic cannot be softened even at high temps?
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Thermosetting materials
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How does a material become thermoset?
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Polymerization of liquid monomers occurs in the presence of a catalyst and heat.
Then the material is cooled (cured) |
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What are some common thermosetting materials?
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CR-39 (allyl diglycol carbonate)
Epoxies |
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What is it called when a type of plastic material is made by combining 2 monomers from one group of plastics or 1 monomer from each group?
When are these often used? |
Copolymer or hybrid material
When offered exclusively by one company (proprietary material) |
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What ophthalmic material offers the greatest impact resistance of all?
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Polycarbonate
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For which types of patients are polycarbonate lenses the standard of care?
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Children, athletes, and certain occupations
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Put the following lens materials in order of increasing impact resistance:
Polycarbonate Crown Glass CR-39 Trivex |
Crown Glass
CR-39 Trivex Polycarbonate |
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Why is trivex a good option at times?
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It has better impact resistance than CR-39 and better optical quality than polycarbonate.
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What do ALL plastic lenses need?
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scratch-resistant coatings
ON both surfaces |
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Besides scratch resistant coatings what other coating SHOULD plastic lenses have?
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AR
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What type of lenses, glass or plastic, are less likely to fog with changes in temperature? Why?
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Plastic
Because plastic has less thermal conductivity than glass. |
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What is the index of refraction of crown glass?
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1.523
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What is the index of refraction of CR-39?
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1.498
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What is the index of refraction of polycarbonate?
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1.586
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What are the two purposes of frames?
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1. Hold lenses in the proper position
2. Cosmetic |
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What does the frame front consist of?
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1. 2 Eyewires
2. Bridge (with nose pads) 3. 2 Endpieces |
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What do the eyewires do?
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They give the frame shape and size
They hold the lenses in place |
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What does the bridge do?
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Supports the frame on the nose either directly or via nosepads
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What do the endpieces do?
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They are the connecting points for the temples via hinges
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What does the temple consist of?
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1. Shaft
2. Bend |
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What is the extent of the shaft?
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It extends from the hinge to the bend
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What does the bend of the temple do?
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It provides support and stability at the ear or skull.
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What are the 2 general types of frame materials?
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Plastic
Metal |
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What is the nickname for all plastic frames? Why is this strange?
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Zyl (short for zylonite which is cellulose nitrate)
Strange because zylonite is banned because of the danger of flammability |
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What is the name of a traditional plastic that is being used less and less?
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Optyl (epoxy resin)
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What are the three types of synthetic plastics used for frames that provide superior strength and are significantly lighter in weight?
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1. Carbon fiber
2. Polyamide 3. Kevlar |
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What are the 3 main metal frame materials?
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1. Nickel silver
2. TItanium 3. Stainless steel |
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What is nickel silver an alloy of?
What are some possible problems? |
Copper, nickel, zinc
Allergic reactions and corrosion |
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What are the pros of titanium?
What are the cons? |
Pros: light weight, hypoallergenic, no corrosion
Cons: expensive, difficult to adjust, hard to repair |
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What are the pros of stainless steel?
What are the cons? |
lightweight, hypoallergenic, less expensive than titanium.
Cons: can get corrosion if plastic materials are used in combo with steel |
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All metal frames have nosepads, what are they usually made of?
What can they be made of if there is an allergy problem? |
Silicone or cellulose acetate
Gold-plated nickel silver |
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What do most nosepad allergies result from?
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Allergens collecting on the nosepads over time
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How often should nosepads be changed?
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Once a year
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What is a form-fit bridge?
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A single solid nosepad that extends over the bridge of the nose.
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Is a form-fit bridge adjustable?
Is that good or bad? |
No
Bad |
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What do plastic frames have instead of nosepads?
Is this adjustable? |
Extensions of or widenings of material On the nasal portion of each eyewire.
No. Take care when fitting. |
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How often should the nylon cord be replaced in a rimless mount frame?
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Every 2 years
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How often should the screws be tightened in a drill mount frame?
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Monthly
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What size frame is better for higher plus or minus lenses?
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Smaller
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What size frame is better for PALs?
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Larger
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Where do most major manufacturers list their frames?
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The Frames Book
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Where on a pair of glasses can you find information about the manufacturer and frame style?
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On the inside of the temple
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About how many small niche companies are there that do not list their frames in the Frames Book?
Where do they typically get exposure? |
1000
Their own catalogs, word-of-mouth, and expos. |
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What is important to take into consideration when helping a patient choose frames?
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Current fashion, patients face, personality, lifestyle
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How can you know what the trends are?
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Pay attention to the newest fashions in movies and the in the news.
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What is the most common system for describing the dimensions of a frame in the US?
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The Boxing System
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Which measurement describes the horizontal distance between the nasal and temporal vertical tangents at the lens bevel? Also known as the eye size of the frame?
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The A measurement
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Which measurement describes the vertical distance between the upper and lower horizontal tangents at the lens bevel?
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The B measurement
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Which measurement describes the horizontal distance between the two nasal vertical tangents? Also known as the bridge size of the frame?
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DBL (Distance between lenses)
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What measurement is given by the intersection of the diagonals of the box? It can also be given by the intersection of the perpendicular bisectors of the A and B dimensions.
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GC (Geometric Center)
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What is the name for the point about which the lens rotates during the edging process?
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The Mechanical Center (often used synonymously with GC)
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What is the distance between the geometric centers of the eyewires?
How else can you calculate this dimension? |
DBC (distance between centers) or frame PD
The A dimension plus the DBL. |
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If you saw the following on a frame, what would it mean?
52 "box" 19 |
It means that the A dimension is 52mm
The DBL is 19mm And therefore the DBC (frame PD) is 52+19 = 71mm |
