3. CL III - CL Material Flashcards
What are the requirements for a contact lens material? (9 points)
- Optically transparent
- Oxygen permeable
- Non-toxic
- Chemically inert
- Wettable
- Inexpensive/abundant
- Easy to manufacture
- Tough
- Low density
What properties do rigid contact lenses specifically need? (7 points)
- Hard
- Not water permeable
- Oxygen permeability
- Wettability
- Deposit resistant
- Durable, stable, minimal flexure (can warp based on removal technique)
- May be surface coated (to prevent deposits)
Describe PMMA and which type of lens it’s mainly used for.
PMMA: ...
Lens type: ...
........................
Describe PMMA and which type of lens it’s mainly used for.
PMMA: poly methyl methacrylate
Lens type: rigid lenses
readily machined and polishedthermoplastic - moulded with head + pressurevery clearlow costeasy to care for<0.5% water contentNO O2 PERMEABILITYonly used for trial lenses
Describe silicone and which type on lens it’s mainly used for.
Lens type: ....
Advantage: ...
Disadvantage: ...; ..., ..., ...
Two types:
-
...-... ...
Describe silicone and which type on lens it’s mainly used for.
Lens type: rigid lenses.
Advantage: Highest Dk
Disadvantage: very hydrophobic; increased deposition, expensive, non-water permeable
Two types:
-
silicone resins-used in aphakic patients due to high oxygen permeability silicone elastomers
Describe silicone acrylate and what type of lens it’s used for.
Lens type: ...
Made from a mix of ...: ...
It has a low to medium Dk ... and is ... now-a-days.
Describe silicone acrylate and what type of lens it’s used for.
Lens type: rigid lenses
Made from a mix of MMA and silicone: MMA backbone with a Si-O-Si bond
It has a low to medium Dk (12-60) and is rarely used now-a-days.
Describe FSA (first generation) and what type of lens it’s used for.
Name: ...
Lens type: ...
It has better ... and ... with the same basic structure as.... It has ... which improve ... and reduce .... It is however more ... and more ....
Describe FSA (first generation) and what type of lens it’s used for.
Name: fluoro-silicone methacrylates
Lens type: rigid lenses
It has better wettability and oxygen transmissibility with the same basic structure as silicone acrylate copolymer. It has fluorinated side chains which improve wetting properties and reduce protein deposition. It is however more susceptible to lipid deposits and more sensitive to harsher cleaning agents.
Describe FSA (second generation) and what type of lens it’s used for.
Name: ...
Lens type: ...
They have ... as well as ... which aim to improve .... Has increased ..., ..., and .... Average Dk values are ... - ... and Dk/t is above .... Common materials are ... and ....
Describe FSA (second generation) and what type of lens it’s used for.
Name: fluoro-silicone methacrylates
Lens type: rigid lenses
They have lower silicone content, 5-7% as well as other monomers which aim to improve oxygen permeability. Has increased wetting, deposit resistance, and material durability. Average Dk values are 40 - 100+ and Dk/t is above 87. Common materials are Boston XO and Menicon Z.
Which materials fall into these Dk categories?
High Dk (31-60)
Super Dk (61-100): ... and ....
Hyper Dk (>100): ... and ...
Which materials fall into these Dk categories?
High Dk (31-60)
Super Dk (61-100): Paragon HDS 100 and Boston XO.
Hyper Dk (>100): Menicon Z and Boston XO2.
Which radiation type to FSA lenses absorb?
UVA and UVB (wavelengths near 400nm).
What are the basics of soft contact lens materials?
Made from ... with ..., designed to help with ...; a .... The water content depends on ... and water .... In its dry state, it’s ..., ..., and .... In its wet state, it’s ... and ....
What are the basics of soft contact lens materials?
Made from PMMA with hydroxyl groups, designed to help with water imbibition; a hydrogel. The water content depends on percentage of hydrophilic and hydrophobic groups in the polymer and water dissolves O2 for Dk effect. In its dry state, it’s hard, glassy, and easy to lathe. In its wet state, it’s soft and flexible.
What are the properties of hydrogel materials?
The Dk is related to ... and average Dk values are ... - .... The surface charge can be ... which ... or ... which .... Its deposit resistance is related to ... and .... It’s water permeable however ... and the lenses can ....
What are the properties of hydrogel materials?
The Dk is related to water content for majority of materials and average Dk values are 8.3 - 38.9. The surface charge can be ionic which attracts protein or non-ionic which is less likely to attract protein as they are surface treated. Its deposit resistance is related to pore size and surface charge. It’s water permeable however dehydration state depends on individual eye and the lenses can also dehydrate the eye.
What are the 4 US FDA material classifications?
Group I: ... and ....
Group II: ... and ....
Group III: ... and ....
Group IV: ... and ....
What are the 4 US FDA material classifications?
Group I: LWC <= 50% and non-ionic.
Group II: HWC > 50% and non-ionic.
Group III: LWC <= 50% and ionic.
Group IV: HWC > 50% and ionic.
Describe HEMA and what type of lens it’s used for.
Made of ... that’s crosslinked with ....
Lens type: ...
It’s part of FDA Group ... with water content of ...%. It has a low Dk, ..., particularly in ... as ...; may result in ....
Describe HEMA and what type of lens it’s used for.
Made of hydroxyethyl methacrylate monomer that’s crosslinked with EGDMA, ethylene glycol dimethacrylate.
Lens type: soft lenses
It’s part of FDA Group I with water content of 38%. It has a low Dk, as low as 10, particularly in high myopic prescriptions as lenses become thicker and thicker; may result in limbal hyperaemia.
Describe higher water content hydrogel materials and what lens it’s used for.
Lens type: ...
Part of Group II when made of ... or part of Group IV when made of ....
Advantages: they have increased .. and ... with longer ....
Describe higher water content hydrogel materials and what lens it’s used for.
Lens type: soft
Part of Group II when made of n-vinyl pyrrolidone, NVP or part of Group IV when made of methacrylic acid, MA.
Advantages: they have increased Dk and thickness for handling ease with longer wear time.
What are the limitations of HWC hydrogels?
They have reduced ... and get more .... They are .... The material has larger ... so ... to avoid .... HWC commonly absorbed the tear film components; Group II have ... and Group IV have ....
What are the limitations of HWC hydrogels?
They have reduced life-span and get more porous as they age. They are more expensive. The material has larger pore size so we're restricted to disinfection materials with large molecule size to avoid disinfectant imbibing. HWC commonly absorbed the tear film components; Group II have lipid deposition and Group IV have protein deposition.
What are the 9 requirements of a contact lens material?
- Optically transparent;
- Oxygen permeable;
- Non-toxic → prevent immune response on the eyes;
- Chemically inert → prevent CLs from biding to the eye;
- Wettable → permit tear flow;
- Inexpensive/ Abundant;
- Easy to manufacture;
- Tough → prevent breakdown due to chemical agents;
- Low density
What are the important properties of a rigid lens material?
- Hard & minimally flexible;
- Not water permeable;
- Oxygen permeability;
- Wettability;
- Deposit resistant → may be coated;
- Durable, stable, minimal flexure
Hydrogels can come in other forms,
* ... (GMA) combined to HEMA or MMA;
* HEMA + ... (MA);
* HEMA+ ... (MMA).
The most common hydrogel material is ...+.... It has a ... charge and is successful as an ..., ... material. A well-known brand of contacts using this material is .... Due to the low ... value of this material, these should not ....
Hydrogels can come in other forms,
* glyceryl methacrylate (GMA) combined to HEMA or MMA;
* HEMA + methacrylate acid (MA);
* HEMA+ methyl methacrylate (MMA).
The most common hydrogel material is HEMA+MMA. It has a neutral charge and is successful as an opaque, tinted material. A well-known brand of contacts using this material is Freshlook Colourblends disposable. Due to the low Dk/t value of this material, these should not be worn everyday.
What could be a consequence of wearing contact lenses to hot springs or saunas?
The extreme temperatures of these environments may alter lens material and adhere to the corneal epithelium, causing the epithelium to be ripped off when removing the CLs. Minerals from hot springs can also deposit onto the CLs and result in corneal reactions.
A type of myopia control CL uses hydrogel in the form of HEMA + `` (PC), which is trade as ... A. PC is a synthetic analogue of a natural ..., which mimics .... It has an approved "..." claim, which "may provide ... from symptoms of ...". Another type is ... (PVA), which is ... in charge and ....
A type of myopia control CL uses hydrogel in the form of HEMA + phosphorylcholine (PC), which is trade as omafilcon A. PC is a synthetic analogue of a natural phospholipid, which mimics cell surfaces. It has an approved "biocompatibility" claim, which "may provide increased comfort from symptoms of dryness". Another type is polyvinyl alcohol (PVA), which is neutral in charge and resist deposition.
Is dry eye symptoms mor common in high water content materials or low water content materials? Why?
Dry eye symptoms are more common in high water content materials. High water content materials attract the polar heads of lipid molecules towards them, leaving their non-polar tails away from the surface of the lens. This leaves the lens surface prone to dewetting and/ or evaporation.
What influences contact lens dehydration? How do hydrogels compare to silicone hydrogels?
CL hydration is influenced by the environment, water content, thickness and wearing time. Hydrogels dehydrates more easily than silicone hydrogel. Refitting daily hydrogel CL wearers into SiHy can reduce dry eye symptoms.
... is the only true high .... ... allows for high ..., thus high ...; whereas ... allow for ..., ... and .... This material is inherently ` …, therefore has the disadvantage of … and increased …, which requires treatment. This material also has a significantly higher … than …`.
Silicon hydrogel is the only true high Dk SCL material. Silicone allows for high oxygen permeability, thus high Dk value; whereas hydrogel monomers allow for flexibility, wettability and fluid transport. This material is inherently hydrophobic, therefore has the disadvantage of poor wettability and increased lipid deposition, which requires treatment. This material also has a significantly higher elastic modulus than hydrogels.
What are the 3 clinical advantages of silicon hydrogels?
- Minimal limbal hyperaemia, corneal neovascularisation or oedema;
- May reduce symptoms of dry eye;
- Water content of 20-40% ensures water transmissibility for rapid recovery from any lens adherences after overnight wear
What are the 2 clinical disadvantages of silicon hydrogels?
- Can still lead to complications similar to hydrogels: GPC, CLARE, CLPUC;
- Higher incidence of mechanical complications, due to high modulus: mucin balls, SEALs (superior epithelial arcuate lesion)
How was the wettability of silicone hydrogel materials improved? What other 2 factors were improved overtime?
SiHy are made to be inherently wettable by moving from surface treatments to internal wetting agents. Improvements were also made to decrease the modulus of the lenses and increase the water content.
As the modulus increases, Dk ... because of the increase in .... The ultimate goal is to achieve ... but with ....
As the modulus increases, Dk increases because of the increase in silicon content. The ultimate goal is to achieve high O2 permeability but with low modulus.
Alcon Total Dailies 1 utilises a “water gradient” silicone hydrogel, what does this mean?
These have a high silicone content core, thus it has a high Dk and low water content in the centre. However the surface of the lens is hydrophilic and has a high water content.
B&L BioTrue one day utilities a “Hypergel” bio-inspired material, named nesoilcon A. What special properties does it have?
This material claims to have an outer surface that mimics the lipid layer of the tear film. It’s water content is made similar to the cornea (78%), with a Dk of 42
