progressive lenses, multifocal lenses, polyfocal lenses, lenses for presbyopia, bifocal lenses, lenses for near reading, lenses for the elderly, above age 40

1. By: Herojit Asem
Progressive Addition Lenses-
Design, Optical & Performances

2. Presentation Layout
 Introduction to PAL
 Structural features and optical characteristics
 Optical description of progressive lenses
 PAL designs
 Special design PALs
 Performance characteristics of PAL
 Prism thinning in PAL
 Lens design selection
 Summary

3. WHAT ARE PROGRESSIVE
ADDITION LENSES?
 A lens designed for presbyopes with power
gradually increasing from the distance zone,
through a progressive zone to the near zone.
 Curvature of surface increases from its minimum
value in distance zone to maximum value in near
zone

4. Curves Contiguous and
Umbilic

5. History of progressive lenses
 1950s Virulux from Essel (now Essilor) by
Bernard Maitenaz
- Hard design, symmetric lens
 1970s Varilux II
- Hard design, asymmetric
 1980s families of lenses ( hard , soft and in-
between)
- Lenses for different patient types or uses
 1990s New soft lenses (multi-design)
- Lenses for all users and adapted to all
prescriptions

6. Progressive power lens offers
 Vision at all distance
 More natural use of accommodation
 No image jump
 Thinner and lighter
 Eye rotation is required to see from distance to
near vision area and head movement is required
to see across the lateral areas of astigmatism

7. STRUCTURAL FEATURES & OPTICAL
CHARACTERISTICS
 Distance zone: A stabilized region in the upper
portion of lens provides the specified distance
prescription.
 Near zone: A stabilized region in the lower portion
of lens provides the specified Add power

8.  Progressive corridor: A corridor of increasing
power connects these two zones and provides
intermediate or mid range vision
 The length of corridor is the distance from the
center of the fitting cross to the position where
85% of the near add is achieved.
 Blending region: The peripheral regions of the
lens contain non prescribed cylinder power and
provide only minimal visual acuity

10. Umbilicus
 A vertex line along which spherical add power
increases towards the bottom of the lens
 Surrounding the vertex line are increasing
amount of unwanted astigmatism
Lens Radius Changes Along
Umbilical Line

11. Minkwitz’s Theorem
 The rate of change in unwanted cylinder power (Δ
Cyl) at a small distance away from the centerline
of progressive corridor is nearly equal to twice the
rate of change in Add power (Δ Add) over an
equal distance along the centerline of the corridor

12.  The average rate of change in Add power along
the progressive corridor is equal to the total add
power divided by the corridor length of lens

13. PAL blank…

14. OPTICAL DESCRIPTION OF
PROGRESSIVE LENSES

15. POWER PROFILE
 The curve represents the power progression of
the lens along its meridional line from distance to
near vision

16. CONTOUR PLOT
 Two dimensional map of the lens representing
either the distribution of power or of astigmatism
 The map shows lines of equal dioptric values
(isopower or iso-astigmatism)
 Between two consecutive lines, the power or
astigmatism varies by a constant values

18. GRID PLOT
 The grid highlights the distribution of prismatic
effects of the lens by showing how they alter a
regular rectangular grid

19. THREE DIMENSIONAL PLOT
 A 3-D representation which plots vertically the
value of a given optical characteristic at each
point of lens in relation to a reference plane
 May be used to show the distribution of power,
astigmatism, prismatic effects, gradients of power
variations
 More demonstrative of lens characteristics than
contour plot

21. PRINCIPAL PARAMETERS OF
PAL

22. PAL DESIGNS
 Hard design
 Soft design
 Symmetrical design
 Asymmetrical design
 Mono design
 Multi design
 Prescription based design

23. HARD DESIGN VS SOFT
DESIGN

24. HARD DESIGN

25. SOFT DESIGN

26. Hard design Soft design
Wide distance and reading zones
Narrow intermediate zones
Close spacing of contour lines
Reduced distance and reading zones
Wider intermediate zone
Wide spacing of contour lines

27. Indication for selection of hard
design and soft design
Hard design :
 Previous successful hard lens wearers
 People who do a lot of reading
Soft design :
 Young presbyopes
 Active outdoor profession
 Professional driver

28. SYMMETRICAL VS
ASYMMETRICAL DESIGN
Symmetrical designs
 Conventional PALs
 Right and left lenses were identical
 The lens blank were rotated 9 to 11° nasally to
achieve the desired near inset

30. Asymmetrical design
 Separate designs for the right and left lenses
 Amount of cylinder power on either side of
progressive corridor is adjusted independently,
which allows the near inset to be achieved
without rotating the lens design
 The progressive corridor is initially designed at an
angle with the necessary nasalward inclination
 Provides better binocular alignment between the
right and left viewing zones with large binocular
field of view

31. Horizontal symmetry
 Lenses were asymmetrical but designed to give
the wearer equal acuities and prismatic effects at
all corresponding points of gaze in order to
achieve excellent binocular vision

33. MONO DESIGN
 It classify hard and soft
 Maintain design principles throughout the range
of addition
 It describe the characteristics of progressive zone
with a range of power for a given design

34. MULTI DESIGN
 In 1988, Essilor introduced PAL that used a
different design for each reading addition
 Incorporates the best features of hard and soft
lenses
 Low reading additions were combined with a soft
design which become harder as the add power is
increased
 The reading area remain almost constant
throughout the range
 Ensure the visual comfort and ease of adaptation
at each stage of presbyopia

35. Progression profile of Multi design PAL

36. PRESCRIPTION BASED
DESIGN
 Dedicated design for every base and add
 Design by base-different designs for hyperopes,
myopes and emmetropes
 Design by add- effective near zone sizes change
as the add increases
 Near inset position varies relative to level of
presbyopia and reading distance
 Corridor length also varies relative to both base
and add.

37. NEW PAL DESIGNS
 Atoric progressives
 Position of wear or as worn lens design
 Personalized progressives
 Internal progressives

38. ATORIC PROGRESSIVES
 Oblique astigmatism can be corrected for
spherical lenses by using an aspheric surface
 But if the lens had two different powers i.e when
prescribed cylinder power is present, then oblique
astigmatism could only be corrected for both
meridians at once if an atoric lens design is used
 In PAL, oblique astigmatism caused by lens
aberration combine with unwanted cylinder in
lens periphery

39.  Free form technology used to produce atoric
surfaces
 Process begins by generating the lens surface
using a three axis computer numerically
controlled (CNC) generator
 With three possible axes of movement, single
point cutting tools can produce any lens surface
with a high degree of accuracy and smoothness
 E.g. Ziess Gradal Individual, Varilux Physio 360

40. POSITION-OF-WEAR OR AS-
WORN LENS DESIGNS
 Includes following factors in the design of lens on
an individual basis
 Pantascopic tilt
 Vertex distance
 An aspheric or atoric surface
 The practitioner specify the sphere, cylinder and
axis measures along with vertex distance and
pantascopic tilt

41.  When the prescription is received, an optimum
base curve is chosen for the front surface of lens
and prescription is modified to allow for tilt and
vertex distance
 Then the amount of asphercity needed in each
major meridian is calculated
 E.g. Rodenstock Multigressiv 2 lens

42. PERSONALIZED
PROGRESSIVES
 Designed to match the unique head and eye
movements of the wearers
 Uses an instrument called VisionPrint System to
measure head and eye movement
 The lens is designed so that the near viewing
area will match the personal viewing habits of the
wearer
 E.g. Varilux Ipseo

44. SPECIAL PURPOSE PALS
 Short corridor progressive lenses
 Near variable progressive lenses
 Occupational progressives that include distance
powers

45. SHORT CORRIDOR
PROGRESSIVE LENSES
 Allows a PAL to be worn in a frame with a small
vertical dimension
 Faster transition from the distance and near
portion of lens
 Wearer is quickly into the near portion when
looking downward
 Minimum fitting height should be suitable for the
frame

46. NEW VARIABLE FOCUS
LENSES
 Started out as a replacement for single vision
reading glasses

48. OCCUPATIONAL PROGRESSIVES
WITH DISTANCE POWER
 Used for small office environments and computer
viewing
 Include a small distance portion located at the top
of lens
 Intermediate area of the lens positioned in front of
eye
 Intermediate and near zones considerably wider
than standard progressives but not as wide as
near variable focus lenses

49.  E.g. AO Technica, Hoya Tact

50. PERFORMANCE
CHARACTERISTICS OF PAL

53. PRISM THINNING IN PAL
 Increase thickness of PAL when the distance
powers are either plus or low minus
 Result of steepening front curve in the lower half
of lens
 To reduce the thickness, base down prism can be
added to whole lens
 a yoked base down prism

55.  The amount of prism needed to thin the lens
varies according to the strength of addition, size
and shape of lens after edging, and design of
lens
 Varilux suggests adding prism power amounting
to approx. two thirds of the power of the add

56. LENS DESIGN SELECTION
Consider how the wearer uses their lenses
 For most wearers a good modern progressive
lens design is the best solution
 But not all designs provide wide fields of view at
distance, intermediate and near
 Consider the design that will suit the wearer
 general purpose : balanced fields of view
 mainly for reading : wide near visual fields
 mainly for computer : wide intermediate visual fields

57. PATIENT SELECTION FOR PAL
Who are good candidate?
 Those who require add power for certain task but
prefer edge not visible
 Presbyope complaining image jump
 Emerging presbyopes
 Person needing trifocal

58. Who are Poor candidate?
 Having motion sickness
 Satisfied with bifocal
 High add requirement(3.00D)
 Significant vertical muscle imbalance
 Anisometropia (>3Ds)

59. SUMMARY
 Any lens for presbyope is a compromise and so is
the
 PALs
 Proper understanding of lens design is important
 Proper coordination with the patient requirements
and lens design selection
 Add power and corridor height

60. REFERENCES
 System for Ophthalmic Dispensing 3rd edition ,
W.brooks, M. Borish
 Clinical Optics 2nd edition, Theodore Grosvenor
 Borish’s Clinical Refraction, William J. Benjamin
 Fundamentals of Progressive Lens Design, Darryl
Miester
 Progressive Addition Lenses, Essilor Academy
 Ophthalmic lenses and dispensing M.O Jalie