Chapter 5- Dispensing part II (2) Flashcards
What is the difference between bifocals and progressive lenses?
Progressive lenses provide the most natural vision for the wearer by seamlessly transitioning between near and far prescriptions within the lens.
Whereas, a bifocal lens is separated into distinct areas of near and far vision prescriptions
What are the advantages of a plastic frame material?
1- More people are less likely to have an allergic reaction to plastic.
2- Less likely to get bent out of shape
What are the disadvantages of a plastic frame material?
1- May be more breakable than a metal frame
2- Requires more frame material to make them than a metal frame so they tend to be heavier.
What are some examples of materials that come with plastic frames?
1- Cellulose acetate
2- SPX
What are the properties of cellulose acetate?
1- Inexpensive
2- Has reinforced sides- metal spike down the sides
3- However, they can discolour with age and can react with skin to form white deposits.
4- Adjusts at moderate heat (57 degrees)
What are the properties of SPX?
1- Flexible
2- Lightweight
3- Adjusts at 95 degrees- however, it can shrink if overheated
What are some of the materials that come with metal frames?
1- Nickel silver
2- Nickel titanium
3- Titanium
What are the properties of nickel silver?
1- Most common metal used for frames – inexpensive
2- Can be easily adjusted
3- Skin can react to nickel
What are the properties of nickel titanium?
1- Lighter than silver nickel
2- Has memory metal (returns to original shape when heated)
What are the properties of titanium?
1- Expensive
2- Lighter than nickel titanium
3- Flexible
4- Hard to repair