Test 1 Review Flashcards
What is the formula for mm to diopter conversion?
D = 337.5 / mm
What is the average HVID?
11.7mm
What is the average VVID?
10.6mm
What is average CCT?
0.52mm
What is average limbal corneal thickness?
0.67mm
What is the average central radius of the cornea?
7.8mm
What is the average sagittal depth of the cornea?
2.6mm
What is the average index of refraction of the cornea?
n = 1.376
What percentage of the cornea is made up of water?
78%
How thick is the corneal epithelium?
50 microns
What ensures the transparency of the stroma?
The lamellar arrangement
Which lenses are made via lathing or molding?
GP
Which lenses are made via cast-molding or spin casting?
SCL
What are some advantages to lathing GP lenses?
Almost unlimited designs
Good for custom lenses
What is the GP manufacturing method of choice?
Lathing
What are some disadvantages to lathing GP lenses?
Slow production
High cost per lens
Labor intensive
What is plasma treatment?
A “super cleaning” using room temperature, ionized oxygen and UV energy to break organic bonds
Which lenses can be plasma treated?
GP
How long does plasma treatment last?
Few days, to months
What is the purpose of plasma treatment?
To increase wettability
What is Dk?
Oxygen permeability
What is the “D” in Dk
Diffusion coefficient
What is “k” in Dk?
Solubility of the gas in the material
What is Dk/t?
Dk value / thickness
What is the necessary Dk/t for DW lenses under open eye conditions?
24
What is the necessary Dk/t for EW lenses under open eye conditions?
87
What is the necessary Dk/t for DW lenses under closed eye conditions?
35
What is the necessary Dk/t for EW lenses under closed eye conditions?
125
What is the required EOP for DW lenses?
9.9%
What is the required EOP for EW lenses?
17.9%
What removes lipids from CLs?
Isopropyl alcohol
Surfactants
What removes proteins from CLs?
Proteolytic enzymes
Surfactants
Proteins are attracted to which type of CL?
Ionic lenses
Lipids are attracted to which type of CL?
Non-ionic lenses
What is the usual percentage of Hydrogen Peroxide in peroxide based cleaners?
3%
How long do lenses need to be left in peroxide to kill acanthomoeba?
3-6 hours
Do multipurpose solutions sterilize lenses?
No - they disinfect and preserve
What is the main difference between the Andrasko and IER staining studies?
Andrasko was measured after 2 hours of exposure
IER was 3 months worth of data
Which type of soft CL is prone to lipid deposits?
Si-Hy
Si-hy lenses are prone to lipid deposits, and what else?
Mucin balls
What damage do mucin balls do to the cornea?
Epithelial dimples, causing NaFl pooling, but not staining
What is PMMA, and some of it’s properties?
Hard lens materia
No Oxygen transmission
Old material
What are the two old, traditional Hard lens materials?
PMMA
CAB
What are the 4 common hard lens materials?
PMMA
CAB
SA
FSA
What is the “standard” soft lens material?
HEMA
What is EGDMA and its properties??
A crosslinking agent for soft lenses that stiffens material and lowers the water content
What does GMA do?
Increases wettability and deposit resistance in SCLs
Why does GMA increase deposit resistance?
Smaller pore size
What does MMA do?
Decreases water content
Increases strength of lens
No Oxygen transmission
What does PVA do?
Increases water content
Increases resistance to deposits
Increases Dk
Increases Strength