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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
Q

Describe Fexon – Memory Metal

A
  • Titanium-based alloy
  • Usually found in the shaft of the temple, and bridge, allowing twisting without breakage
25
Q

Describe Fexon – Memory Metal

A
  • Titanium-based alloy
  • Usually found in the shaft of the temple, and bridge, allowing twisting without breakage
26
Q

What are the advantages & disadvantages of Fexon – Memory Metal

A

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
Q

Describe Stainless Steel frames

A
  • Alloy of iron, nickel, manganese, chromium
  • Not too expensive
28
Q

Advantages & disadvantages of stainless steel frame

A

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
Q

Describe multifocals

A
  • These are lenses in which there are two (bifocals) or three (trifocals) distinct portions of different focal power
30
Q

Advantages & disadvantages of Franklin Bifocal

A

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
Q

What are 7 different types of bifocal?

A
  1. Round seg
  2. Flat top
  3. Executive
  4. Curved top
  5. Ribbon Seg
  6. A seg
  7. Blended seg
32
Q

Describe round seg

A
  • 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
Q

Describe Flat-Top/D-Seg

A
  • 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
Q

Describe Curved-Top/Panoptik

A
  • Look similar to flat-top, however the upper line is curved
  • Much less common than flat tops
35
Q

Describe Ribbon Seg

A
  • 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
Q

Describe Executive for bifocals

A
  • 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
Q

Describe A segment for bifocals

A
  • 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
Q

Describe blended segment for bifocals

A
  • Very much the same as a round seg, with the edges blended for cosmetic appearance
39
Q

Who would wear Bifocals?

A
  • 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
Q

Who are not Suitable to wear Bifocals?

A
  • New presbyopes
  • Image conscious people
  • Unstable walkers
  • Successful progressive or trifocal lens wearers
41
Q

Who are not Suitable to wear Bifocals?

A
  • New presbyopes
  • Image conscious people
  • Unstable walkers
  • Successful progressive or trifocal lens wearers
42
Q

Advantages vs Disadvantages for Bifocals

A

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
Q

What is Seg Magnification

A
  • The seg being a positive lens will magnify an image, with higher the seg power, more the resultant magnification
44
Q

What is an image jump?

A
  • 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
Q

What are the four types of trifocals?

A
  1. Flat top
  2. Executive
  3. E-D
  4. Round seg
46
Q

Describe Flat-Top for trifocals

A
  • 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
Q

Describe Executive Trifocal

A
  • 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
Q

Describe E-D Trifocal

A
  • Combines an executive with a flat-top lens
  • Excellent for working at a desk
49
Q

Describe round seg for trifocals

A
  • ‘Bulls-eye’ appearance
50
Q

Who would wear Trifocals?

A
  • Presbyopes
  • Older patients
  • Handymen
  • Chefs
  • Computer use
51
Q

What are the two main methods for construction of glass bifocals?

A
  1. Fused bifocal
  2. One-piece bifocal
52
Q

Describe Cemented Bifocal

A
  • 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
Q

Describe One-Piece Bifocal

A
  • 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
Q

Describe Fused Bifocal

A
  • 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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