Patent ID: 8857990

Claim:
A progressive addition lens demonstration device for demonstrating a variety of different progressive addition lenses to permit a patient to experience a variety of distance vision fields and reading vision fields, said device comprising: A) a frame adapted to hold in place in front of each of a patient's eyes three lens mounts, defining a third lens mount, a first lens mount and a second lens mount, at least the second and third lens mounts being adapted for adjustment in rotation and side-to-side translation, B) a third lens displaying the patients base prescription mounted in the third lens mount, C) a first and second lens mounted respectively in the first and second lens mounts said first and second lenses, each having a transition zone and a power ramp zone and having complementary surfaces so that when stacked together they create a standard progressive addition lens with a distance vision field, a reading vision field and transition region, and when the first or second lenses are moved or rotated the locations of the distance vision field, the reading vision field and the transition region are adjusted allowing the patient to experience a variety of distance vision fields, reading vision fields, and transition regions; wherein for the first lens, the form of the power ramp zone is a spiraling power, which is expressed in polar coordinates approximately by the thickness function: T lens1 ( r ,θ)≈ Cr 2 (θ−θ 1 )+ T 0 ,θ∈power ramp and the form of the transition zone is: T lens1 ( r ,θ)≈ r 2 ƒ(θ)+ T 0 ,θ∈transition zone where T 0 is a base thickness, θ is a base orientation, C is the ramp steepness and the function f(θ) is picked to smoothly transition the two edges of the transition zone so that there is no discontinuity in the thickness, and also no discontinuity in slope and where the form of the power ramp zone for the second lens is complementary to the form of the power ramp zone for the first lens, and the form of the transition zone for the second and third lenses have the same functional form.