16. Contact lens material Flashcards
What are some Ideal RGP material properties?
- Optically transparent
- Easy to manufacture
- Cheap
- Hard
- Dimensional stable
- Limited flexure
- Inert
8, Wettable - Deposit resistant
- Scratch resistant
- Durable
- Good oxygen permeability
What was the 1st material used to manufacture RGPs? And why was it discontinued?
PMMA
Discontinued because: 0 oxygen permeability and very rigid- poor comfort and corneal moulding.
What is cellulose acetate butyrate? (CAB)
Plastic made with cellulose base used in RGP lens making
How is the Dk value of CAB?
Low
The difference in terms of protein in CAB and silicone acrylates?
CAB does not attract protein, silicone acrylates attract protein
Describe the Dk of silicone acrylates?
Low- medium
What is found within Flurosilicone acrylate?
Fluorine monomer added to silicone acrylate
How does addition of fluorine help in Fluorosilisone acrylate?
It improves wettability, tear film stability, deposit resistance and Dk
Fluorosilisone acrylate Dk value?
Very high
When silicone was added to lenses what else needed to be added along with it?
A wetting agent because it is very hydrophobic- to help tear film stabilize over it.
Advantage of high water content hydrogels
- Higher patient comfort
- Higher wettability
- Increased oxygen permeability (Dk)
- More flexible, lower modulus
Disadvange of high water content hydrogels
- Fragile, easy to tear
- Difficult to handle
- More on eye dehydration
- Greater deposition
- Difficult to manufacture
- Must be made thicker
Advantages of low water content hydrogels?
- Higher modulus can make lens easy to handle.
- Less breakage, longer lifespan.
- Less on eye dehydration.
- Higher refractive index.
- Thinner lenses.
- Easy to manufacture.
Disadvantage of low water content hydrogels?
- Lower Dk
- Higher modulus
- Less wettable
- Less comfortable
