DISP Flashcards
What are the refractive indices for plastic complex lenses?
1.6, 1.67, 1.74 with MAR
What are the refractive indices for glass complex lenses?
1.7, 1.8, 1.9 with MAR
How does refractive index affect density and aberration in lenses?
As refractive index increases, density and amount of aberration increases, while weight decreases for plastic and increases for glass.
What effect does reducing lens diameter have?
It reduces weight and thickness.
Why is it important to match HCD to PD?
To reduce the need for decentration.
What is the influence of high refractive index materials on lens thickness?
In full aperture lenses, they have much more influence on thickness than aspheric lenses.
What are the benefits of aspheric lenses?
Better optics over +7.00D, better cosmetic appearance due to flatter front surface, increased FoV. Better cosmetic appearance for minus lenses too.
What are lenticular lenses?
Lenses where the effective optical aperture is smaller than the frame aperture.
What are the uses of lenticular lenses?
Used to reduce weight and thickness of high powered lenses, but have poor cosmetic appearance and reduced FoV.
What types of lenticular lenses are there?
Standard lenticular and blended lenticular.
What are the types of bifocal and multifocal forms for negative lenses?
Bifocal and progressive up to -12.00D.
What characterizes classic progressive power lenses?
Stable distance power in the top half, stable reading area in the bottom central area, and a progressive power corridor joining the two zones.
What are the characteristics of soft multifocal lenses?
Longer progression lengths, aspheric distance curves, small stable distance and near zones, low surface astigmatism.
What are the characteristics of hard multifocal lenses?
Shorter progression lengths, spherical distance curves, larger stable distance and near zones, higher surface astigmatism.
What is prism thinning in lenses?
Incorporated vertical prism to reduce thickness and weight of lens with no relative prismatic effect.
