Design and History of Progressive Add Lenses

Where does the name Progressive Add Lens (PALs) come from?

- from a zone of progressive increase in power from a stable distance portion to a stable near portion of the lens

What do PALs lack?

No segment line → no image jump.

TRUE/FALSE: All PALs have unwanted astigmatism in the periphery of the lens.

TRUE! This is due to blending aspheric surfaces

Where do we get differences between the various styles of PALs?

differences in the design priority

- distance size, near size, etc.

What is the progression of a PAL zones from top to bottom?

• Distance at the top

• progressive corridor

• near reading portion at the bottom

What are some advantages of PALs?

- clear vision at all viewing distances

- no visible reading segment

What is a disadvantage of a PAL that we cannot seem to avoid?

astigmatism in transition zones due to aspheric surfaces joining distance and near portions of the lens

What are the two broad categories of PALs?

- hard designs

- soft designs

Characteristics of hard designs.

• short and rapid increasing power corridor

• wide distance and near portions

• large amounts of astigmatism present in the periphery of lens

• more “swim effect”

• better for advanced presbyopes

Characteristics of soft deigns

• longer, wider corridor

• narrower distance and near portions

• less peripheral astigmatism → less severe so easier adaptation

• ideal for early presbyopes

Interrelated parameters of PALs

- size of distance and near zones

-length of corridor

- location of aberrations

What was the first successful PAL in the US?

Onmifocal lens - 1961 by D. Volk and J. Weinburg

What is the design concept of the Omnifocal Lens of 1961?

- vertical curvature increased downward

- no change in the horizontal meridian radius of curvature

- LED to plus cyl axis @ 90

What were problems with the Omnifocal lens?

• required compensating cyl on the back

• same semifinished blank OD/OS so you have to rotate nasalward

• large progression zone —> soft design

• difficult so replaced by Varilux

Which lens was the most success commercially design?

Varilux I

Who did Varilux I lenses in 1959?

- Essilor

- the upper half of the lens had no progression in power

- 12 mm deep corridor w linear progression of power

What was the varilux comfort?

a successful PAL that refined the multi-design lens

• excellent balance of wide usable zones and low astigmatism

What was the essilor Ipseo?

• used a sensor device to classify patients as :

• eye movers, head movers, or mixed movers

What was noted about Varilux 2 in 1972?

- entire front aspheric surface

- family of conic sections

- softer than Varilux I so better adaptation!

What was the varilux Infinity?

• THE FIRST MULTI-DESIGN PAL (different design for each add power instead of one design for all)

Why was the Varilux Infinity Multi-Design PAL important?

Add demands change visually. Infinity recognized this and adapted for each add.

American Optical did the Ultraview lens of 1973, what was special about it?

- hard design

- concentrated design efforts on getting a large astig-free distance and near optics

- had to rotate lens to get right and left versions

Which lens has less peripheral astigmatism but was a hard design?

Truevision of 1982 by American Optical

What were the lenses by American Optical?

- Ultraview

- Truevision

- Truevision Omni

Which lens was based on the Dirichlet Principle of theramal gradients of two points on a thin copper sheet?

TrueVision Omni which was a soft design

What was the 10/30 PAL of 1978?

- 10 mm deep progressive corridor

- 30 mm wide usuable segment area

- hard design

- nonlinear progression zone

What is the CPS lens?

a soft cosmetic parabolic sphere lens