2. Definition –
The power of addition gradually increases as the line of
the vision sweeps downward through the lens.
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Progressive Addition Lens
3. Benjamin Franklin invented first bifocal
spectacle lens in 1784.
First patient on progressive power lenses
was published in 1907 by Owen Ave.
Forerunner of Essilor company introduced first
commercially available PAL Varilux 1, in 1959.
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History
8. All PALs contain important markings which are
used to identify lenses & to assist in their
fitting & verification .
- Permanent Marking
- Ordinary Marking
8
PALs Markings
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62.0
10. Distance & near reference points for power measurement
Fitting cross for fitting purposes
Prism reference circle for prism measurement between
lenses
Micro etching for re-marking purposes
Peripheral lens aberration in peripheral zone
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PALs Marking
11. Power progression by increasing the front surface
curvature from dist to near zone
Rate of power progression determines the length of
intermediate zone
The position of the near zone is offset nasally
(convergence for near)
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Optical Design
12. Design in PAL’S :
Hard design
Soft design
Advanced soft design
Symmetrical design
Asymmetrical design
Mono design
Multi design
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13. Hard design –
Rapid progression from dist to near power
Large dist & near zone ( free of aberration area)
Shorter & narrower intermediate zone
More adaptation time
People who do a lot of reading
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PALs Design Categories
14. Soft design –
Slower progression from dist to near power
Smaller dist & near zone ( free of aberration area)
Longer & wide intermediate zone
Less adaptation time
Young presbyopes
Active outdoor profession
Professional driver
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PALs Design Categories
16. Advanced soft design –
The progression zone is similar to a hard design
Larger effective distance and near zones
Unwanted cylinder(induced astigmatism)is pushed
towards the periphery similar to a soft design.
Therefore giving wider and larger intermediate zone
Peripheral aberrations are very well controlled, so the
wearer gets adapted very easily
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PALs Design Categories
18. Pattern of PAL’s
Symmetrical PAL
Identical right & left lenses
Lens rotation of two eyes is equal & same amount ( i.e.
10º )
Nasal decent ration of near zone
Imbalance can cause more difficult wearer adaptation
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19. Pattern of PAL’s
Asymmetrical PAL
Incorporated a nasal offset of near zone
Negates the lens rotation
Leading to better adaptation & visual comfort
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20. The other design considerations are …...
Multi-design Vs Mono-design :
In Multi-design the position for the near vision
changes with the addition power increase end
the near area goes up with the increase in the
addition which improves the comfort of the
wearer
In Mono design the position of the near vision
doesn’t change with the addition powers- thus
causing difficulty while viewing near
objects/prints as the wearer holds the reading
material closer to him as his add power increases
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22. Fitting Progressive Lenses
When fitting progressive lenses, use the following
procedure:
1. Select the frame
2. Pre-adjust the frame
3. Measure the fitting heights
4. Measure the distance PDs
5. Verify lay-out card
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23. Dispensing PALs – Frame selection
Metal frame with adjustable pads is a good option.
Frame height require to ensure adequate area for distance
& near.
- at least 18 mm below and
- at least 14 mm above from the pupillary center.
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24. Pre-Adjust the Frame
Ensure a minimal vertex
distance
Ensure at least 7° or
more of Pantoscopic tilt
Ensure a sufficient
amount of face-form
wrap
Adjust frames with
demo lenses in place
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25. Effect of Vertex Distance
Shorter vertex distances increase the field of view
through the viewing zones of the lens.
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26. Effect of Pantoscopic Tilt
Pantoscopic tilt brings the near zone closer to the eye and
increases the field of view through the near zone of the
lens
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27. Effect of Face-Form Wrap
Face-form wrap increases the field of view through
the distance zone of the lens.
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28. PD measurements
Monocular PD is more important.
Measures from the center of nose to the center of the
pupil.
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29. PD measurements
Methods include
Pupillometer
Direct pupillary reflex marking method.
PD ruler
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30. Verify cut-out card
Use the correct cut-out
card for the lens design
Place the dotted demo
lens on the fitting point
of the Lay out card, and
ensure that the frame will
cut- out at the desired
measurements
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31. Frame Verification
Verify frame level with lay-out card followed PD markings.
Make sure that frame is suitable for PAL, before fitting.
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32. Key points to success with PALs
An accurate refraction.
Correct size of frame and
adjustments
An accurate monocular PD
measurements.
Perfect fitting.
Proper instruction on use.
Motivate the patient to adapt the
new type of vision.
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33. Advantages of PAL
No visible segments.
Continuous field of clear vision
Comfortable intermediate vision
Continuous support to eye’s accommodation
Continuous perception of space
Lighter & thinner than single vision of the same power
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36. Extreme right picture shows clear intermediate vision
through progressive lens
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37. Using the distance vision
portion of a bifocal
Using the near vision segment
of a bifocal
Using the intermediate
portion of a progressive
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39. Straight line appears curved
Adaptation required
Peripheral aberration
More steps in fitting
Increase in eye and head movement
Eye must be dropped a longer distance
Expensive compared to bifocals
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Disadvantages of pal
40. Bifocal
Provide distance &
near vision only
Distinct junctions
between zones
Lower cost
Fast fitting procedure
Prismatic image jump
Cosmetically
unappealing
PALs
Provide intermediate
vision also
No visible junctions
between zones
More cost
More steps in fitting
No prismatic image jump
Cosmetically appealing
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Bifocal vs. PALs
