wk4: CL/M - Soft and RGP Materials Flashcards
List 9 requirements of contact lens materials
optically transparent
non-toxic
chemically inert
oxygen permeable
wettable
inexpensive/abundant
easy to manufacture
tough
low density
Why do we want contact lenses to be tough?
so they can last for however long they are scheduled for
What contact lenses don’t require cleaning/disinfection?
daily disposables
List 5 important properties of rigid lenses
oxygen permeability
wetting of material
deposit resistant
durable, stable, minimal flexure
may be surface coated - more fragile
How does the wetting of a rigid lens material vary with silicone content
inversely influenced
Is PMMA thermosetting or thermoplastic?
thermoplastic (i.e. moulded with heat and pressure)
Describe the quality of the optical clarity provided by PMMA material
excellent
In regards to PMMA:
- how expensive?
- what percentage water content?
- how much O2 permeability?
cheap
0.2-0.5% water content
zero O2 permeability
Which lens material has the highest Dk?
Silicone lenses
What are the limitations of silicone lenses? (4)
very hydrophobic
therefore increased deposition and poor wetting
expensive
non-water permeable
Are silicone RGPs used today?
No. Because of their limitations
How commonly are silicone acrylates used today as lens materials?
they aren’t
List 2 limitations of silicone acrylates
poor wetting deposits
flexure problems
What is the purpose of fluoro-silicone methacrylates (FSA) lenses? (2)
aimed to improve the wettability and oxygen transmissibilty
What benefits do the fluorinated side chains provide to FSA lenses? (2)
Improve wetting properties
Reduce protein deposition
List 2 downsides to 1st gen FSA lenses
More susceptible to lipid deposits
More sensitive to harsher cleaning agents
How do 2nd gen FSA materials compared to 1st gen FSA materials? (4)
improved wetting and deposit resistance
improved material durability
higher Dk
improved potential for extended wear
State the range of Dk values you can get for 2nd gen FSA materials?
40-100+ (mid-high dk)
What is the Dk/t for 2nd gen FSA materials? How does this relate to extended wear?
Dk/t >87, meaning these materials havepotential for extended wear
Name 5 examples of 2nd gen FSA materials
boston xo
menicon z
fluorex 500
fluoroperm
paragon hds 100
How does the silicone content of 2nd gen FSA materials compare to other FSA materials? Why?
Lower silicone content (5-7%) with the use of other monomers for oxygen permeability
Most modern FSA lenses absorb near to what wavelength?
near to 400nm (so UVA and UVB)