Aspheric Lenses Flashcards
What is different about an aspheric lens compared to a spherical lens?
Aspheric lenses have a changing radius of curvature, spherical lenses have a constant radius of curvature
What are the types of conic section?
Circle
Ellipse
Parabola
Hyperbola
What classifies the type of asphericity used?
P-value
A smaller p-value means that the lens is…
flatter
What does Tscherning’s ellipse indicate?
The BC needed for the minimal amount of oblique astigmatism
What advantages does an aspheric lens have over a spherical lens?
Flatter lens reduces magnification
Thinner and lighter lens
Abberations from the lens are optically corrected
Lens will fit better into frame due to reduced BC
What are the types of lens design?
Aspheric
Atoric
Spherical
How is an aspheric lens constructed?
F1: Aspheric
F2: Spherical or toric
How is a spherical lens constructed?
F1: Spherical
F2: Spherical or toric
How is an atoric lens constructed?
F1: Spherical
F2: Atoric
What does atoric mean?
Lens surface is aspheric, but by varying amounts in each meridian to account for astigmatism
How can you add prism to an aspheric lens?
Has to be ground into lens
How can you identify an aspheric lens?
Lens clock
Grid pattern
Compare lens curvature to known spherical lens of same power
When should you consider dispensing an aspheric lens?
> +/-3.00D power
Anisometropics with over 2.00D difference
Cyl >2.00D (atoric)
What are the differences between a full aspheric and a non-full aspheric lens?
Full: aspheric curves begin close to centre and increase more peripherally. If lens decentred, results very noticeable (worse than decentre spherical lens).
Non-full: central area is spherical, curves start to change further out. Decentration not as noticeable compared to full aspheric.
