wk4: CL/M - Soft and RGP Materials

Question 1

List 9 requirements of contact lens materials

Answer 1

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

Question 2

Why do we want contact lenses to be tough?

Answer 2

so they can last for however long they are scheduled for

Question 3

What contact lenses don’t require cleaning/disinfection?

Answer 3

daily disposables

Question 4

List 5 important properties of rigid lenses

Answer 4

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

Question 5

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

Answer 5

inversely influenced

Question 6

Is PMMA thermosetting or thermoplastic?

Answer 6

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

Question 7

Describe the quality of the optical clarity provided by PMMA material

Answer 7

excellent

Question 8

In regards to PMMA:
- how expensive?
- what percentage water content?
- how much O2 permeability?

Answer 8

cheap
0.2-0.5% water content
zero O2 permeability

Question 9

Which lens material has the highest Dk?

Answer 9

Silicone lenses

Question 10

What are the limitations of silicone lenses? (4)

Answer 10

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

Question 11

Are silicone RGPs used today?

Answer 11

No. Because of their limitations

Question 12

How commonly are silicone acrylates used today as lens materials?

Answer 12

they aren’t

Question 13

List 2 limitations of silicone acrylates

Answer 13

poor wetting deposits
flexure problems

Question 14

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

Answer 14

aimed to improve the wettability and oxygen transmissibilty

Question 15

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

Answer 15

Improve wetting properties
Reduce protein deposition

Question 16

List 2 downsides to 1st gen FSA lenses

Answer 16

More susceptible to lipid deposits
More sensitive to harsher cleaning agents

Question 17

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

Answer 17

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

Question 18

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

Answer 18

40-100+ (mid-high dk)

Question 19

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

Answer 19

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

Question 20

Name 5 examples of 2nd gen FSA materials

Answer 20

boston xo
menicon z
fluorex 500
fluoroperm
paragon hds 100

Question 21

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

Answer 21

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

Question 22

Most modern FSA lenses absorb near to what wavelength?

Answer 22

near to 400nm (so UVA and UVB)

Question 23

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

Answer 23

increases contrast

Question 24

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

Answer 24

% of hydrophilic to hydrophobic groups in polymer

Question 25

What is PMMA material used for?

Answer 25

ONLY USED FOR TRIAL LENSES

Question 26

How is water conent and Dk related?

Answer 26

water dissolves O2 for Dk effect

Question 27

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

Answer 27

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

Question 28

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

Answer 28

pore size surface charge

Question 29

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

Answer 29

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

Question 30

Is HEMA ionic or non ionic?

Answer 30

non-ionic

Question 31

In regards to HEMA: - water content? - Dk level?

Answer 31

38% water content (low/moderate) Low Dk

Question 32

How commonly is HEMA used today?

Answer 32

rarely

Question 33

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

Answer 33

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

Question 34

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

Answer 34

increased Dk and improved physiology, longer WT Increased thickness for improved handling

Question 35

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

Answer 35

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

Question 36

List 6 limitations of HWC materials

Answer 36

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

Question 37

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

Answer 37

Group II: mainly lipid deposition Group IV: mainly protein deposition

Question 38

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

Answer 38

II: non-ionic IV: ionic

Question 39

Name 2 characteristics of GMA combined with HEME or MMA

Answer 39

low dehydration, low deposition

Question 40

What type of deposition does HEMA and Methacrylic acid have?

Answer 40

protein deposition

Question 41

Which hydrogel material is sensitive to pH?

Answer 41

HEMA and Methacrylic acid (MA)

Question 42

What is HEMA and MMA known for?

Answer 42

sucessfl as an opaque tinted material

Question 43

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

Answer 43

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

Question 44

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

Answer 44

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)

Question 45

How much deposition do PVA materials get?

Answer 45

they resist deposition

Question 46

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

Answer 46

Group II material

Question 47

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

Answer 47

Silicone hydrogels

Question 48

What are the hydrogel monomers in silicone hydrogels important for?

Answer 48

allowing CL movement

Question 49

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

Answer 49

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

Question 50

List 3 advantages of silicone-hydrogels

Answer 50

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

Question 51

List 3 disadvantages of silicone-hydrogels

Answer 51

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

Question 52

Briefly describe the 3 generations of silicone hydrogels

Answer 52

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

Question 53

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

Answer 53

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

Question 54

What is modulus?

Answer 54

= stiffness vs water content

Question 55

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

Answer 55

Significantly higher than hydrogels, making them stiffer