Session 4 Flashcards
Practice 5 examples of finding the Nominal Power.
How is a spherical lens made with a rx of just sph?
Front and Back surface is spherical
How is a spherical lens made with a rx of sph and cyl?
Front surface is spherical
Back Surface is toric
What is a spherocylindrical lens?
Made of sphere and cyl each with a different radius of curvature. Meridians are at 90 degrees and has two different focal points and images.
Name 2 types of Spherocylindrical lens?
Plus Cylinder Form
Minus Cylinder Form
How is a Plus Cylinder Spherocylindrical lens made?
Front surface = two curves (Base curve + Cross Curve)
Back Surface = Sphere curve/Spherical
What is the difference between Cross Curve and Base curve in a plus spherocylindrical lens?
Cross Curve is the stronger or steeper of the two curves.
Base Curve is the weaker or flatter of the two curves.
How is a Minus Spherocylindrical lens made?
Front Surface = Base Curve (spherical curve)
Back surface = two curves (Cross curve + Toric Base Curve)
What is the difference between the Cross Curve and the Toric Base Curve
Cross curve is the stronger or steeper of the two.
Toric Base Curve is the weaker or flatter of the two.
Look at examples in Powerpoint and practice 5 examples of different spherocylindrical lens prescriptions and identify the curves.
Name 7 Forms a Lens can take.
Meniscus (Plus/Minus)
Biconvex
Biconcave
Equiconcave
Equiconvex
Planoconcave
Planoconvex
What are 3 types of lens designs
Spherical Based Lenses
Aspheric Lenses
Atoric Lenses
What is a spherical lens design?
Consistently curved surface made from perfect sphere. Power is the same in all meridians.
What is a Aspheric lens design?
Where the surface flattens gradually across the vertical and horizontal meridians.
How is a Aspheric lens designed if the rx is just sph?
Front Surface = Aspheric
Back Surface = Spherical
