progressive lenses, multifocal lenses, polyfocal lenses, lenses for presbyopia, bifocal lenses, lenses for near reading, lenses for the elderly, above age 40
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
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
9.
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
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
17.
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
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
29.
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
32.
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
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
43.
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
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
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
54.
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