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Clinical Optics and Dispensing > Week 5: Frame Materials/Adjustments & Multifocals > Flashcards

Week 5: Frame Materials/Adjustments & Multifocals Flashcards

1
Q

List seven different plastic frames

A
  1. Cellulose acetate
  2. Cellulose propionate
  3. Polyamide
  4. Optyl
  5. Carbon fibre
  6. Nylon
  7. Polycarbonate
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2
Q

Describe Cellulose Acetate

A
  • Best quality plastic
  • Frames are cut from an acetate sheet
  • Sheets are pre-coloured prior to cutting
  • Labour intensive – 120 steps in the manufacturing process
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3
Q

Advantages & disadvantages of Cellulose Acetate

A

Advantages:
- Non-flammable
- Polishes well (maintains glossy appearance for long time)
- Colour-fast
- Easily repaired
- Acetate can be marginally shrunk if lenses have been cut too small

Disadvantages
- Plasticisers will deteriorate with time, forming a white film on the surface
- Small cracks may develop in frame
- Frame becomes brittle after exposure to sun or extreme heat
- May return to normal flat shape with time, or with extreme heat

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4
Q

Describe Cellulose Propionate

A
  • Injected moulded
  • Less labour intensive
  • Less ‘off-cuts’ - ↓ waste material
  • Requires more plasticisers, hence less stable & more heat sensitive
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5
Q

Advantages & disadvantages for Cellulose Propionate

A

Advantages:
- Slightly thinner & lighter than acetate
- Less expensive to produce
- Frames can be made & coloured later
- Better shape retention
- Hypo-allergenic

Disadvantages:
- Needs more heat than acetate for adjustments
- Cannot be shrunk
- Surface dye may become buffered off
- Tends to become brittle with age, sun & excessive heat

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6
Q

Describe Polyamide

A
  • Injection-moulded, however plasticisers are not required
  • Nylon-based material (strong & flexible)
  • Do not need to be heated to make fitting/adjustments
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7
Q

Advantages & disadvantages of Polyamide

A

Advantages:
- Very lightweight
- Good shape stability
- Hard surface
- Heating not required for adjustments and fitting
- Hypo-allergenic

Disadvantages:
- Overheating can result in shrinkage

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8
Q

Describe Optyl

A
  • Thermo-setting material
  • Difficult to overheat
  • Approximately 30% lighter than cellulose acetate
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8
Q

Advantages & disadvantages of Optyl

A

Advantages:
- Returns to original shape regardless of heating
- Does not age & become brittle
- Much lighter than most other plastics
- Hypo-allergenic
- Patterned/coloured after production

Disadvantages:
- Can be difficult to adjust
- Should not be cooled too quickly
- Adjustments will be lost if frame left in car/heat
- Ageing and exposure to sunlight decreases strength
- Colour can fade

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9
Q

Describe Carbon Fibre

A
  • Injection-moulded
  • Flexible nylon compound mixed with a fibre or whisker
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10
Q

Advantages & disadvantages of Carbon Fibre

A

Advantages:
- Lightweight
- Good shape retention & strength
- Hypo-allergenic

Disadvantages:
- Carbon fibre is quite brittle when dropped
- Difficult to fit and adjust carbon fibre frames
- Poor range of colours available
- Can break frame when fitting new lenses

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11
Q

Describe Nylon

A
  • Most basic of the nylon-plastics
  • Injection-moulded
  • Typically used for safety specs and sunglasses
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12
Q

Advantages & disadvantages of Nylon

A

Advantages:
- Very strong and flexible
- Lightweight
- Not affected by heat and cold

Disadvantages:
- Poor surface finish
- Extremely difficult to adjust & to fit lenses
- Can be brittle
- Can only be manufactured in dark colours

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13
Q

Describe Polycarbonate

A
  • Primarily used for safety specs and sports glasses
  • If made with no prescription, the lens + frame are often moulded into one unit
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14
Q

Advantages & disadvantages of Polycarbonate

A

Advantages:
- Very impact resistant
- Can be used as shield over top of specs

Disadvantages:
- Poor surface finish – dull and not polished
- Extremely difficult to adjust and to fit lenses
- Can be brittle

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15
Q

List 5 different metal frame material

A
  1. Gold-filled
  2. Gold-plated
  3. Nickel Silvers
  4. Titanium
  5. Stainless steel
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16
Q

Describe Gold Frames

A
  • Gold is mixed with other metals to produce an alloy
  • Most ‘gold frames’ contain very little gold
  • There are two processes for attaching the gold layer to the base metal;
  • Gold-filled
  • Gold-plated
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17
Q

Describe gold filled frames

A
  • Layer of gold is brazed onto the surface of the base metal & becomes bonded. The frame is then produced
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18
Q

Advantages & disadvantages of gold filled frames

A

Advantages:
- High quality – tarnish & perspiration resistant
- Easy to adjust & align
- Very durable & maintain appearance

Disadvantage:
- Quite expensive

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19
Q

Describe Gold-Plated frames

A
  • The base metal frame is produced, then suspended in an electrolyte bath with gold applied by electrolysis to the frame
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20
Q

Advantages & disadvantages of Gold-Plated frames

A

Advantages:
- High quality – tarnish & perspiration resistant
- Easy to adjust & align
- Very durable, & maintain appearance
- Easier and cheaper to produce than gold-filled frames

Disadvantages:
- Slightly more susceptible to corrosion from perspiration
- Still relatively expensive

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21
Q

Describe Nickel Silvers

A
  • Contains more than 50% copper, 25% nickel and rest zinc – no silver
  • Copper gives pliability, zinc adds strength, and nickel gives the whitish appearance
  • May be most commonly found in hinges, end pieces, bridges and the inner core of temples
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22
Q

Describe titanium frame

A
  • Metal frame of choice today!
  • Very light, very strong, and very expensive
23
Q

What are the advantages & disadvantages of Titanium frames?

A

Advantages:
- Very strong
- Lightest of metals (40% lighter than most metals)
- Hypo-allergenic
- Holds adjustments well

Disadvantages:
- Very expensive
- Difficult to repair – cannot be soldered
- Restricted range of colours

24
Describe Fexon – Memory Metal
- Titanium-based alloy - Usually found in the shaft of the temple, and bridge, allowing twisting without breakage
25
Describe Fexon – Memory Metal
- Titanium-based alloy - Usually found in the shaft of the temple, and bridge, allowing twisting without breakage
26
What are the advantages & disadvantages of Fexon – Memory Metal
Advantages: - Return to original shape, even after twisting or bending - Lightweight - Hypollargenic - Corrosion-resistant - 25% lighter than standard metals Disadvantages: - Can be difficult to adjust
27
Describe Stainless Steel frames
- Alloy of iron, nickel, manganese, chromium - Not too expensive
28
Advantages & disadvantages of stainless steel frame
Advantages: - Strong, so can be made extremely thin and light weight - Highly flexible/springy temples - Low toxicity - Hypoallergenic (if no nickel) - Resistant to corrosion, abrasion & head Disadvantages; - Difficult to adjust, solder or weld
29
Describe multifocals
- These are lenses in which there are two (bifocals) or three (trifocals) distinct portions of different focal power
30
Advantages & disadvantages of Franklin Bifocal
Advantages: - Distance and near optical centres being able to be placed in any desired position Disadvantages: - Not very durable - Poor cosmetically - Collects dirt along the ridge between the segments
31
What are 7 different types of bifocal?
1. Round seg 2. Flat top 3. Executive 4. Curved top 5. Ribbon Seg 6. A seg 7. Blended seg
32
Describe round seg
- The reading portion forms a perfect circle - Optical centre of the segment is at the exact centre of the seg - Typically the seg diameter is 24mm, although can be from 22 to 40mm
33
Describe Flat-Top/D-Seg
- Most popular design - Similar to a round seg, with the top ‘cut-off’ - Is made in glass (fused) or plastic (one- piece) – hence the ridge in CR-39 - OC typically 5mm below the seg line - Typically D-28 (mm) or D-35
34
Describe Curved-Top/Panoptik
- Look similar to flat-top, however the upper line is curved - Much less common than flat tops
35
Describe Ribbon Seg
- Like a flat-top, with the bottom of the seg also cut-off - 2 types; - B-seg (9mm deep) - R-seg (14mm deep) - May be used for near prism control
36
Describe Executive for bifocals
- Always one-piece construction (glass or CR-39) - ‘Shelf’ between the two sections - May be better to prescribe a large flat-top (D-35
37
Describe A segment for bifocals
- Like a large round seg - Two spherical surfaces on one side of the lens - Always one-piece - Plastic: reading curve moulded on front of lens - Glass: bifocal placed on back, therefore needs a plus-cyl on front surface - Diameter is 38mm for glass & 40mm for plastic
38
Describe blended segment for bifocals
- Very much the same as a round seg, with the edges blended for cosmetic appearance
39
Who would wear Bifocals?
- Presbyopes or people with accommodative problems - Previous wearers - Unsuccessful progressive lens wearers - Some children with accommodative problems, esophoric myopes - Patients with economic restrictions - Some occupations
40
Who are not Suitable to wear Bifocals?
- New presbyopes - Image conscious people - Unstable walkers - Successful progressive or trifocal lens wearers
41
Who are not Suitable to wear Bifocals?
- New presbyopes - Image conscious people - Unstable walkers - Successful progressive or trifocal lens wearers
42
Advantages vs Disadvantages for Bifocals
Advantages: - Convenience – not changing between specs - Cheaper than buying two separate pairs of specs - Less likely to lose specs - More convenient for handicapped presbyopes - Children who use lenses for accommodative control can find near seg more easily Disadvantages: - Aesthetically not ideal - Implicitly associated with age - Image jump
43
What is Seg Magnification
- The seg being a positive lens will magnify an image, with higher the seg power, more the resultant magnification
44
What is an image jump?
- Is also known as “differential displacement” - It is the difference in location of objects observed when transitioning between distance & near segments - If a px wearing bifocals move their gaze from the distance portion to near portion of the lens, the image will appear to shift up
45
What are the four types of trifocals?
1. Flat top 2. Executive 3. E-D 4. Round seg
46
Describe Flat-Top for trifocals
- Depth of intermediate portion is typically 7mm - If trifocal is fused, the intermediate portion will have a refractive index between that of distance & near glass
47
Describe Executive Trifocal
- Depth of intermediate portion is typically 7mm - If the trifocal is fused, intermediate portion will have a refractive index between that of the distance & near glass
48
Describe E-D Trifocal
- Combines an executive with a flat-top lens - Excellent for working at a desk
49
Describe round seg for trifocals
- ‘Bulls-eye’ appearance
50
Who would wear Trifocals?
- Presbyopes - Older patients - Handymen - Chefs - Computer use
51
What are the two main methods for construction of glass bifocals?
1. Fused bifocal 2. One-piece bifocal
52
Describe Cemented Bifocal
- The main lens contains the distance power, and a wafer is the near segment - Near power is the power of the distance portion plus the power of the segment
53
Describe One-Piece Bifocal
- Bifocals may be constructed as a one piece of same refractive index - Usually made of plastic - These lenses are constructed out of a single piece of lens material, with the increase in near power resulting from a change in the curvature in the front surface of the lens
54
Describe Fused Bifocal
- Segment of the bifocal is made of a glass of higher refractive index than the distance ‘carrier’ lens - The segment is fused into the lens such that no change in curvature can be felt on the front surface

Clinical Optics and Dispensing (10 decks)

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