CL Materials Flashcards
What is a CL polymer made up of?
Hydrocarbon backbone
Hydroxyl groups
Oxygen
Nitrogen
Chlorine
(Silicone for SiH)
What properties does a long-chain polymer give CLs?
Toughness and elasticity
What properties does crosslinking of the polymers give CLs?
Increased stability
What helps to make a hydrogel lens hydrophilic?
Hydroxyl group attached to backbone binds with water to form hydrogel
What percentage of a pHEMA (hydrogel) lens is water when fully hydrated?
40%
How is water transported through a hydrogel lens?
Through the water channels
Why might copolymers be added to hydrogel lenses?
To increase water content and therefore oxygen permeability
To alter wettability, modulus and ionicity
What are some common copolymers that may be added to hydrogels?
PVA
PVP
MMA
If the water content is higher in a hydrogel, what can happen as a result?
Quicker dehydration (bc more water needed for lens to be fully hydrated), so reduced wettability and quicker dryness
How do you increase the oxygen permeability in a hydrogel lens?
Make lens thinner
Increase water content
What can packaging additives help with and what are some examples of them?
Increase comfort on insertion
e.g. surfactants and lubricants
How can lubricants and wetting agents help?
Maintain wettability
Reduce dehydration
Increased comfort
What two methods of incorporating lubricants and wetting agents are there?
Binding to the lens material
Releasing from lens material on blink (time release/blink activated)
What are the advantages of high water content hydrogels?
Better oxygen permeability
Reduced rates of hypoxia
Hydrophilic surface
Lower modulus (softer and more flexible)
What are the disadvantages of high water content hydrogels?
Dehydrate more quickly
Reduced wettability (results in more deposition)
Harder to handle and tear more easily due to lower modulus
Difficult to manufacture
Need to be made thicker to compensate for lower modulus (this decreases oxygen permeability)
