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OD2 Semester 2 - Applied Clinical Training > wk4: CL/M - Soft and RGP Materials > Flashcards

wk4: CL/M - Soft and RGP Materials Flashcards

1
Q

List 9 requirements of contact lens materials

A 
optically transparent
non-toxic
chemically inert
oxygen permeable
wettable
inexpensive/abundant
easy to manufacture
tough
low density
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2
Q

Why do we want contact lenses to be tough?

A

so they can last for however long they are scheduled for

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3
Q

What contact lenses don’t require cleaning/disinfection?

A

daily disposables

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4
Q

List 5 important properties of rigid lenses

A 
oxygen permeability
wetting of material
deposit resistant
durable, stable, minimal flexure
may be surface coated - more fragile
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5
Q

How does the wetting of a rigid lens material vary with silicone content

A

inversely influenced

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6
Q

Is PMMA thermosetting or thermoplastic?

A

thermoplastic (i.e. moulded with heat and pressure)

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7
Q

Describe the quality of the optical clarity provided by PMMA material

A

excellent

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8
Q

In regards to PMMA:

  • how expensive?
  • what percentage water content?
  • how much O2 permeability?
A

cheap
0.2-0.5% water content
zero O2 permeability

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9
Q

Which lens material has the highest Dk?

A

Silicone lenses

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10
Q

What are the limitations of silicone lenses? (4)

A

very hydrophobic
therefore increased deposition and poor wetting
expensive
non-water permeable

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11
Q

Are silicone RGPs used today?

A

No. Because of their limitations

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12
Q

How commonly are silicone acrylates used today as lens materials?

A

they aren’t

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13
Q

List 2 limitations of silicone acrylates

A

poor wetting deposits

flexure problems

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14
Q

What is the purpose of fluoro-silicone methacrylates (FSA) lenses? (2)

A

aimed to improve the wettability and oxygen transmissibilty

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15
Q

What benefits do the fluorinated side chains provide to FSA lenses? (2)

A

Improve wetting properties

Reduce protein deposition

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16
Q

List 2 downsides to 1st gen FSA lenses

A

More susceptible to lipid deposits

More sensitive to harsher cleaning agents

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17
Q

How do 2nd gen FSA materials compared to 1st gen FSA materials? (4)

A

improved wetting and deposit resistance
improved material durability
higher Dk
improved potential for extended wear

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18
Q

State the range of Dk values you can get for 2nd gen FSA materials?

A

40-100+ (mid-high dk)

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19
Q

What is the Dk/t for 2nd gen FSA materials? How does this relate to extended wear?

A

Dk/t >87, meaning these materials havepotential for extended wear

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20
Q

Name 5 examples of 2nd gen FSA materials

A 
boston xo
menicon z
fluorex 500
fluoroperm
paragon hds 100
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21
Q

How does the silicone content of 2nd gen FSA materials compare to other FSA materials? Why?

A

Lower silicone content (5-7%) with the use of other monomers for oxygen permeability

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22
Q

Most modern FSA lenses absorb near to what wavelength?

A

near to 400nm (so UVA and UVB)

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23
Q

What is the benefit of a wratten filter for UV absorbing lenses?

A

increases contrast

24
Q

What does the water content of a soft contact lens material depend on?

A

% of hydrophilic to hydrophobic groups in polymer

25
Q

What is PMMA material used for?

A

ONLY USED FOR TRIAL LENSES

26
Q

How is water conent and Dk related?

A

water dissolves O2 for Dk effect

27
Q

Describe the Dk of hydrogel material. What values of Dk would you expect?

A

related to water content for majority of materials (Dk 8.3-38.9)

28
Q

What is deposit resistance of hydrogel materials related to? (2)

A

pore size

surface charge

29
Q

What is the preffered option for hydrogel lens properties? (out of the 4 groups in US FDA material classification)

A

Group II: HWC >50% and non ionic (HWC = high water content)

30
Q

Is HEMA ionic or non ionic?

A

non-ionic

31
Q

In regards to HEMA:

  • water content?
  • Dk level?
A

38% water content (low/moderate)

Low Dk

32
Q

How commonly is HEMA used today?

A

rarely

33
Q

Why might peripheral corneal hypoxia occur with HEMA lens materials? What does this cause?

A

due to lower water content and lower oxygen supply. Causes VEGF signalling causing blood vessels and hyperaemia at limbus

34
Q

List 2 advantages of higher water content hydrogel material (other than higher water content lol)

A

increased Dk and improved physiology, longer WT

Increased thickness for improved handling

35
Q

Why do you need to take care to remove protein when using HWC materials?

A

because HWC tends to absorb more tear film and tends to deposit more protein

36
Q

List 6 limitations of HWC materials

A 
Reduced life span 
Variable degree of dehydration
Slightly higher costs
Larger material pore size
Absorption of tear film components
Dry eye?
37
Q

What type of deposition does HWC group II and IV result in? (2)

A

Group II: mainly lipid deposition

Group IV: mainly protein deposition

38
Q

Is HWC group II ionic or non-ionic? What about group IV?

A

II: non-ionic
IV: ionic

39
Q

Name 2 characteristics of GMA combined with HEME or MMA

A

low dehydration, low deposition

40
Q

What type of deposition does HEMA and Methacrylic acid have?

A

protein deposition

41
Q

Which hydrogel material is sensitive to pH?

A

HEMA and Methacrylic acid (MA)

42
Q

What is HEMA and MMA known for?

A

sucessfl as an opaque tinted material

43
Q

What is phosphorylcholine (PC)? Name a hydrogel material containing PC

A

synthetic analogue of a natural phospholipid that mimics cell surfaces.
HEMA + PC

44
Q 
Which FDA group and ionic/non-ionic are the following materials?
HEMA
GMA with HEMA or MMA
HEMA + MA
HEMA + MMA
HEMA + PC
PVA
A

HEMA: group 1 (non-ionic)
GMA with HEMA/MMA: group I and II (non-ionic)
HEMA + MA: group IV (ionic, -vely charged)
HEMA +MMA: group II (non-ionic)
HEMA + PC: group II (non-ionic)
PVA: group II (non-ionic)

45
Q

How much deposition do PVA materials get?

A

they resist deposition

46
Q

Which FDA group of lens material does data suggest is better for dry eye?

A

Group II material

47
Q

Which lens materials are considered the only true high-Dk SCL materials? (1)

A

Silicone hydrogels

48
Q

What are the hydrogel monomers in silicone hydrogels important for?

A

allowing CL movement

49
Q

List 3 characteristics (and 2 sub-characteristics) of silicone hydrogels

A 
High dk (oxygen permeability)
Inherently hydrophobic (poor wetting, increased lens deposition)
Higher elastic modulus than hydrogels without silicone (therefore stiffer)
50
Q

List 3 advantages of silicone-hydrogels

A

Minimal limbal hyperaemia, corneal neovasc, or oedema
May also reduce symptoms of dry eye
Water content of 20-40% ensures water transmissability for rapid recovery from any lens adherence after overnight wear

51
Q

List 3 disadvantages of silicone-hydrogels

A

Other EW complications such as GPC, CLARE, CLPUC
Higher incidence of mechanical complications
Highlights that factors other than O2 are still important

52
Q

Briefly describe the 3 generations of silicone hydrogels

A

1st gen: plasma-treated, high modulus
2nd gen: no coatings, higher Dk for water content
3rd gen: break traditional water-Dk-modulus relationships

53
Q

What was used on 2nd generation silicone hydrogels as an internal wetting agent? Why?

A

PVP (provides a hydrophilic layer on the surface of the material)

54
Q

What is modulus?

A

= stiffness vs water content

55
Q

Do SiH contact lenses have a higher or lower elastic modulus compared to hydrogel? Are they more or less stiff?

A

Significantly higher than hydrogels, making them stiffer

OD2 Semester 2 - Applied Clinical Training (63 decks)

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