Characteristics Of Ophthalmic Lenses Flashcards
Name the advantages of Glass Lenses
- Superior optics
- Super Scratch Resistant
- Chemically Resistant
Name the Disadvantages of Glass Lenses
- Doesn’t filter UVA or UVB
- Not impact resistant
- Thick and extremely heavy
- Possible to shatter
How are glass lenses created?
By heating and melting materials to a crude finish which has to be roughed down and polished to an acceptable finish
How are Fixed Tints added to Glass lenses?
By mixing special crystals with the “clear” crystal in the process that is then baked in specially designed ovens that results in not only the color but a permanent filter in the lens
Is there any filter with Artificial tints on Glass Lenses?
None
What are the standard Indices of Glass Lenses?
Standard 1.62, 1.70, and 1.80
What does CR39 stand for?
Columbia Resin which took 39 tries to invent it
What are the advantages of CR39 lenses?
- Half the weight of Glass
- Can withstand high temperatures
- Less expensive
- Accepts Tints easily
- 5-10x stronger then glass
What are the disadvantages of CR39?
- Not UVA/UVB filtered
- Not impact resistant
- Thickest of all plastic, non-glass, lenses
What are the advantages of Polycarbonate lenses?
- Thin and Lightweight
- Impact resistant
- UV protection
- 5-20x stronger than plastic
- Abrasion resistant coated
What are the disadvantages of Polycarbonate Lenses?
- Small number of people indicate their vision seems distorted through poly lenses
- Not very thin for high prescriptions
- Hard to tint
Which lens material is used for Blackhawk helicopters?
Trivex lenses
What are the advantages Trivex lenses?
- High tensile strength
- Chemical resistance
- Lightweight
- Impact and abrasion Resistant
- UV protection
- 5-20x stronger than plastic
- Crisp clear optics
- Great for drill mounts
What are the disadvantages of Trivex lenses?
Thicker than poly, but thinner than CR39
What is the Index of Trivex lenses?
1.53
What is the Index of Polycarbonate?
1.59
What are the standard indices of High Index lenses?
1.60, 1.67, 1.70, 1.74
What are the Advantages of High Index Lenses?
- Lighter lenses bc they’re made of less material.
- UV Protection
- Good for strong Rx’s
- Suitable for semi-rimless frames
- Better cosmetic appeal
- Eyes typically appear less magnified/minimized in plus/minus lenses
What are the Disadvantages of High Index lenses?
- Higher cost for the practice and the patient
- Not as lightweight or impact resistant as poly or trivex
- Higher Index of refraction which makes ABBE value worse
- 1.70/1.74 not suitable for drill mount frames
- reflects more light
What is another name for ABBE value?
V - value
What does ABBE Value measure?
a lens materials dispersion of light
When the ABBE Value of a lens is low, what does that mean for the separation of color?
the separation of color is greater
The greater the separation of color, what effect does it have on the image the eye sees?
image becomes distorted due to the inability of the lens to focus all colors onto the same focal point
Does Trivex have more or less unwanted abberation then Poly, and how much?
trivex has less, 35% less
