Review article on Progressive Addition Lens

1. Review Article: on Progressive
Addition Lens
Moderator
Sanjeeb K. Mishra
Sarmila Acharya
Final Year, B.Optometry
Institute of Medicine

2. • Introduction
• Designs
• Lens design to improve Patient’s need
• Eye and head movement with PAL
• PAL for computer Vision
• Adaptation
• Analysis
• PAL wearer’s satisfactory survey
• Discussion
• Conclusion

3. Introduction
• Progressive addition lenses (PAL) are corrective lenses used in
eyeglasses to correct presbyopia and other disorders of
accommodation.
(Advance designs of progressive addition lenses over conventional,
Debapriya Mukhopadhyay, B.V.P.U)
• PAL enables a continuous clear vision at a distance,
intermediate and near in which the dioptric power will
gradually increase along the lens surface from the upper to the
lower portion (Odjimogho, 2004)

4. • There is a continuous downward transition of lens power
from a stable distance power in the upper portion of the
lens through a progressive zone to a stable near vision
portion in the lower area of the lens.

5. • Curvature of surface increases from its minimum value
in distance zone to maximum value in near zone

6. • There is no visible reading segment
• No any dividing line between distance and near portion
• No image jump
• 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
(Advance designs of progressive addition lenses over conventional,
Debapriya Mukhopadhyay, B.V.P.U)

7. • PALs blend the transition between the distance and
near zones to provide addition power without any
segment lines or ledges
• Blending is achieved by incorporating plus-cylinder
at an oblique axis to join sections of two surfaces with
different curvatures in the lateral regions of the lens
surface

9. 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
• Progressive corridor: A corridor of increasing power
connects these two zones and provides intermediate or mid
range vision
• 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
Umbilical
line
Distance
Zone
Near
ZoneIntermediate
Zone
Lens Radius Changes Along
Umbilical Line

11. • In PALs, the continuous change of defocus over the lens
induces peripheral astigmatism which increases
progressively outside the corridor
J.E.Sheedy,C.Campbell,E.KingnSmith,J.R.Hayes,Progressivepowered lenses:
theMinkwitztheorem,Optom.Vis.Sci.82(2005)
• It is not possible to produce a progressive spherical power
surface without astigmatism and distortion being present
at some point
G.Minkwitz, ¨ Uber denFl ¨achenastigmatisms beigewissensymmetrischen
Aspharen,Opt.Acta10(1963)

12. Minkwitz’s Theorem
The rate of change in unwanted cylinder power (∆ Cyl) at a
small distance away from the centerline of progressive
corridor is nearly equal to twice the rate of change in Add
power (∆ Add) over an equal distance along the centerline
of the corridor
G.Minkwitz, ¨ Uber denFl ¨achenastigmatisms beigewissensymmetrischen
Aspharen,Opt.Acta10(1963)

13. • 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
∆ Add = Add power
Length of corridor

14. The rate of change in cylinder power away
from the progressive corridor increases as the
length of the progressive corridor decreases
The rate of change in cylinder power away
from the progressive corridor increases as the
Add power of the lens increases

15. PAL Designs
• Hard design
• Soft design
• Symmetrical design
• Asymmetrical design
• Mono design
• Multi design
• Prescription based design

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

17. Symmetrical designs vs Asymmetrical Design
Greater temporal eye rotation from a central point
RL

18. Progression profile of Multi design PAL

19. Advance designs of progressive
addition lenses
• In traditional designs, the progression is built into the front
surface, and the person's distance prescription is ground
onto the back surface.
• Only adequate for low prescriptions with right and left eyes
with similar powers and low astigmatism (cyl power)

20. • New advanced designs are customised to every type of
prescription as the progression is created with the person's
prescription onto the back surface.
• This results in vision which has less distortions, less swim
effect and consistently wider distance, intermediate and
reading zones.
• This digitally surfaced (free form) design is ideal for mid-
high prescriptions, different right and left powers, reading
adds greater than +1.50, and cyls over 1.00D.

21. Wave front technology
• Wave front technology is the most advanced technology used
in progressive lenses.
• The process involves identifying the lower and higher order
aberrations induced by a lens of a given design, prescription,
and material and then fine-tuning the design to eliminate or
reduce those aberrations that affect visual acuity and quality
of vision.

22. Wavefront-optimized Progressive Performance
Sharpend Distance Acuity
• Higher Order Aberrations, particularly coma, are often present in the
distance field of PAL that creates visual distortion and limits the
sharpness of focus
• Advanced Wavefront optimized PAL provides 3 times less higher order
aberration at distance
Wider Intermediate Vision
• Decreases the amplitude of induced astigmatism on either side of the
progressive channel and directs its axis to a vertical position, which is
more easily “ignored” by the human visual system
• 30% wider

23. Extended near Vision
• Subtle variations in sphere power occur along the length of the
near zone can cause eye strain
• Controls the power distribution and reduces the maximum
defocus by 10%
• enhances wearers’ viewing comfort by extending the vertical
reach of the reading zone and making it more uniform in power
Enhanced Contrast sensitivity
• increases contrast sensitivity by up to 30% by decreasing the
HOAs particularly in low-light conditions

24. Special Purpose Progressive Addition Lenses
• COSMOLIT P; a lens for those who having excessive near
and intermediate work.
• GRADAL RD; solely for intermediate and near vision
activities.
• OVERVIEW; a modified progressive lens designed for those
who perform close work above the eye level.
• READABLES; are lenses that extend the range of clear vision
for near and intermediate vision tasks.
• TECHNICA; is designed to increase the size of the
intermediate lens power area.
(Advance designs of progressive addition lenses over conventional, Debapriya
Mukhopadhyay, B.V.P.U)

25. 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

26. Progressive addition lenses: matching
the specific lens to patient needs
• There are an infinite number of possible PAL designs
because they are designed with surfaces (usually the front
surface) across which the curvatures change.
• There are differences in the occupational and/or
recreational visual needs of presbyopic patients.
• Clinically, it would be useful to match the patient needs
with a PAL design to meet those needs.
Progressive addition lenses matching the specific lens to patient needs, James E.
Sheedy, O.D., Ph.D,The Ohio State University. College of Optometry. Columbus,
Ohio, Optometry ,volume 75,2004

27. Guidelines in selection of lenses based
on patients' visual needs
Distance power zone
• The width of the distance zone at the level of the fitting
cross is particularly meaningful to vision with the eyes in
the straight-ahead position.
• The utility of distance zone width depends on the extent to
which the eye rotates to use peripheral portions of the lens.
• Eye movement occurs before head movement in response to
appearance of lateral fixation stimuli.
Uemura T, Arai Y, Shimazaki C. Eye-head coordination during lateral
gaze in normal subjects. Acta Otolaryngol 1980

28. • For lateral stimuli at 10 and 20 degrees, initial target
acquisition was entirely with eye movement. However, the
final resting eye rotations were 2 and 5 degrees, respectively.
• The final resting position of the eyes can be up to 19 degrees
to one side (38 degrees total, considering both lateral
directions) and the initial eye movement can be up to 40
degrees to one side (80 degrees total).
• Because 1 mm on the lens surface equates to 2 degrees of eye
rotation, the final and initial eye movements require distance
zone widths of 19 and 40 mm, respectively.

29. Intermediate zone
• The validity of these measures can be investigated by analyzing
the visual needs of viewing a computer display.
• A 19-inch computer display, tilted 10 degrees away at the top
and at a viewing distance of 60 cm, subtends a horizontal angle
of 35.7 degrees and a vertical angle of 26.8 degrees.
• The entire display subtends a solid visual angle of 956.8
degrees₂. A quarter of the screen therefore subtends 239.2
degrees2. These convert to a need for 17.85-mm zone width to
fixate both edges of the display and 59.8 mm2 of lens surface to
fixate 25% of the screen.

30. Near zone:
• The validity of these measures can be investigated by analyzing
the visual needs of reading.
• A standard 8.5" x 11“ piece of paper tilted 20 degrees away at the
top and viewed at 40 cm subtends 30 degrees horizontally and 37
degrees vertically. This represents a solid angle of 1,110 degrees2-or
555 degrees2 to fixate half of the page.
• Fixating either side of the page requires a near zone width of 15
mm, and being able to fixate half of the page requires 139 mm2
of lens surface.

31. • The utility of the near zone is dependent on the amount of the
lower part of the lens that remains after edging (i.e., it depends on
the fitting height in the frame).The near zone should, therefore,
be evaluated down to the lowest usable portion of the lens for
different fitting heights.
• A 14-mm vertex distance results in 1 mm on the lens surface
equating to 2 degrees of visual space.
• The visual angles of clear vision through a PAL can be increased
with a shorter vertex distance.
• An 11-mm vertex distance results in 1 mm equating to 2.2 degrees,
whereas a 16- mm vertex distance results in 1 mm equating to 1.85
degrees.

32. • Measurements and analyses clearly indicate that some designs,
based on their optical properties, provide better distance zones,
intermediate zones, near zones, or reduced astigmatism.
• The magnitudes of PAL zone widths and areas have also been
shown to be smaller than the eye fixation demands of those
tasks assuming no adaptive head movements.
• The results and analyses presented in this study can be used to
select particular lens designs that will optimally meet the
specific visual needs of the individual patient.
(Progressive addition lensesmatching the specific lens to patient needs,James E.
Sheedy, O.D., Ph.D.,The Ohio State University. College of Optometry. Columbus,
Ohio)

33. Eye and Head Movements with Single-Vision
and Progressive Addition Lenses
• PAL wearers increase the amount of head movement and
decrease the amount of eye movement used to view a task
as compared to SVL.
• The narrow intermediate zone of clear vision may cause an
increase in the frequency of compensatory head
movements, which is thought to be a major contributor to
non acceptance of PALs.
(Cho MH, Benjamin WJ. Correction with multifocal spectacle lenses. In:
Benjamin WJ, ed. Borish’s Clinical Refraction. Philadelphia: WB Saunders; 1998)

34. • In an attempt to provide clear retinal imagery of the text
through the narrow optical zone, the observer has to
maintain the viewing distance relatively constant and must
also learn to execute appropriate and purposeful lateral eye
and head movements concurrently.
• There occurs the increased frequency and amplitude of
head movements with PALs ( Jones et al.,2003)

35. Static Aspects of Eye and Head Movements during
Reading in a Simulated Computer-Based Environment
Single-Vision and Progressive Lenses
(Ying Han,Kenneth J. Ciuffreda, Arkady Selenow, Elizabeth Bauer,1 Steven R.
Ali,and Wayne Spencer, IOVS, January 2003)
PURPOSE
• To compare the eye and head movement patterns of two
different intermediate progressive lens designs with
movement patterns with a conventional single vision lens
in a computer-based work environment

36. Parameters for vertical eye and head movements
1) maximum amplitude of vertical eye movement per line
2) maximum amplitude of vertical head movement per line
3) total amplitude of maximum vertical eye and head
movements per line
4) maximum amplitude of torsional head movement per line.
For reading rate, the parameters were
1) fixations per 100 words. Fixations refer to the number of
pauses of the eyes during reading
2) the number of progressive or rightward saccadic eye
movements per 100 words
3) the number of regressive or leftward saccadic eye movements per
100 words
4) the number of words per fixation
5) reading rate (number of words per minute)
6) number of return-sweep saccades per overall return-sweep
movement

37. Results
For the horizontal head and eye movements
(1) Head movement was greater with the PALs than with the
SVL
(2) The sum of the amplitude of progressive saccadic eye
movements was greater with the SVL than with the PALs
(3) The difference in amplitude between the return-sweep
saccades and sum of progressive saccades was greater
with the PALs than with the SVL
(4) The total amplitude of head movement and return-sweep
saccades was greater with the PALs than with the SVL for
(5) The percentage of maximum head movement to return-
sweep saccade gaze change was smaller with the SVL than
the PALs, and thus head movement was greater with the
PALs

38. For vertical eye movement and the vertical and torsional
head movements
1) Vertical head-movement amplitude was greater with the
PALs than with the SVL
2) The total amplitude of the combined head and eye
movements was greater with the PALs than with the SVL for
the double-page format
3) Torsional head movement was greater with the PALs than
the SVL for the single-page text format
4) There was a greater number of head movements per line
with the PALs than with the SVL

39. For the reading eye-movement parameters
1) Reading rate was significantly lower with the PALs than
with the SVL
2) The number of return-sweep saccades per line was
higher with the PALs than with the SVL for the double-
page format
3) The number of fixations per 100 words was higher with
the PALs than with the SVL
4) The number of regressions per 100 words was higher
with the PALs than with the SVL

40. Fig; Eye (horizontal, vertical) and head (horizontal, vertical, and torsional) movement recordings

41. Fig. Horizontal eye- and head movement recordings

42. Conclusion
• The percentage of head movement embedded within the mean
total gaze change was greater for the PALs than the SVL.
• There were more combined eye–head movements with the PALs
than with the SVL.
• This may be responsible, in part, for patients’ complaints of
transient confusion, shifting to the wrong new line, “fatigue,” and
perhaps even some optical “swim” sensation during reading.

43. • Reading eye movement parameters were more sensitive to the
lens types. Subjects consistently performed better with the SVL
than the PALs.
• Thus, although PALs have many advantages, such as cosmesis and
convenience, there may be some oculomotor and reading-based
disadvantages to be considered.
• Visual performance should improve in the future, with PALs
having an even wider intermediate zone and overall improved
optics

44. Progressive addition lenses for general
purpose and for computer vision
• Computer vision syndrome comprises many ocular causes,
including the reduced accommodation in presbyopic
computer users, who require spectacle lenses with a near
vision addition to clarify their vision for computer work.
• General purpose PALs; with continuous clear vision
between infinity and near reading distances
• Computer vision PALs; with a wider zone of clear vision at
the monitor and in near vision but no clear distance vision

45. • Head inclination when looking at the monitor was
significantly lower by 2.3 degrees with the computer vision
PALs than with the general purpose PALs.
• Vision at the monitor was judged significantly better with
computer PALs, while distance vision was judged better
with general purpose PALs.
Comparison of progressive addition lenses for general purpose and for computer
vision: an office field study, Wolfgang Jaschinski* Dr Ing, Mirjam König* Dipl
Ing (FH),Tiofil M Mekontso* Dipl Stat, Arne Ohlendorf† Dr Sc Hum, Monique
Welscher§ Dipl Ing (FHClin Exp Optom 2015

46. • Factors that affects dissatisfaction of Computer vision PALs:
1) The size of the screen used may also play a role in source of
dissatisfaction. For example, if larger screens or several screens are
used, a computer vision PAL or a single vision lens with a wider
zone of clear vision may be favoured as it may facilitate task
performance.
2) The frequency with which computer work is alternated with other
occupational activities, such as meetings and customer
consultation or phases of distance vision, may also affect whether
the user wishes to wear a computer vision PAL, which necessitates
changing lenses for distance viewing and they may prefer a more
general purpose PAL instead.
(Selenow A, Bauer EA, Ali SR, Spencer LW, Ciuffreda KJ. Assessing visual
performance with progressive addition lenses. Optom Vis Sci 2002)

47. • The advantage of computer vision PALs was correlated with
several aspects of complaints (‘Vision at the monitor’, ‘Ocular
strain’, ‘Musculoskeletal strain’ and ‘Dizziness’), most of the
participants reported considerable advantages to computer vision
PALs.
(Comparison of progressive addition lenses for general purpose and for computer vision: an
office field study, Wolfgang Jaschinski* Dr Ing, Mirjam König* Dipl Ing (FH),Tiofil M
Mekontso* Dipl Stat, Arne Ohlendorf† Dr Sc Hum, Monique Welscher§ Dipl Ing (FHClin Exp
Optom 2015)
• The preference of lens type between general purpose and
computer vision PALs for presbyopic correction depends on the
individual optometric parameters, the requirements of the
occupational task and user preferences.
• To minimise musculoskeletal strain and to maximise visual
function, the monitor position should be placed within the
vertical zone of clear vision that depends on the optical lens
characteristic when a favourable head posture is maintained.

48. Comparison of Bifocal and Progressive
Addition Lenses on Aviator Target Detection
Performance
• Markovits AS, Reddix MD, O'Connell SR, Collyer PD. Comparison of bifocal and
progressive addition lenses on aviator target detection performance. Aviat. Space
Environ. Med. 1995.
Objective
• to determine if the type of presbyopic correction worn by
aviators, conventional bifocal versus progressive addition
lenses (PAL's), differentially affects aviator visual search
performance.

49. Results
• Latency of locating high-contrast targets under mesopic lighting
condition was differentially affected by the type of presbyopic
correction used.
• Specifically, compared to a standard bifocal, a PAL correction
significantly lowered the time needed to locate static targets at a
cockpit instrument viewing distance (83 cm).
• Accuracy of target location responses was not affected by the type of
correction used.
• Relative to bifocals, speed of responding to static targets at
intermediate viewing distances may be improved by wearing PAL's,
and that subjects were able to adapt to PAL lenses quickly in a
laboratory setting, using them later in a functional aviation
environment

50. Conclusions
• Aviators are required to view critical information at a minimum of
three accommodation distances (approach plate, cockpit
instruments, and infinity).
• Bifocals have only 2 focal lengths; 20 feet (infinity) and, usually, 40
cm, a fairly standard reading distance.
• Trifocals although offering a correction for three viewing distances,
necessarily have a relatively small intermediate segment (vertically),
preventing a full view of the cockpit instruments
• So, the PAL correction is best option for Aviators though some
Aviators are uncomfortable with the head movements that are
needed to accommodate changes in focal length

51. Adaptation to Progressive Additive
Lenses: Potential Factors to Consider
Objective
• to investigate whether the ability to modify the vergence and
phoria systems is significantly different between presbyopes
who could not adapt to PALs and presbyopes who have
successfully adapted to PALs and wear them regularly.
Adaptation to Progressive Additive Lenses: Potential Factors to Consider Tara L.
Alvarez, Eun H. Kim & Bérangère Granger-Donetti,31st May 2017

52. • Maddox described vergence to have tonic, proximal, blur and
disparity inputs.The two main inputs to the vergence system are
accommodation (via blur) and disparity.
• As accommodative convergence decreases with the onset of
presbyopia the role of disparity-vergence gains importance in the
maintenance of single binocular vision.
• Also the phoria adaptation, or the ability to sustain consistent eye
alignment in the presence of a binocular stimulus, may also be a
primary factor in maintaining stable and comfortable binocular
vision.
• The change in the magnitude of phoria reduces the load on the
disparity convergence system.

53. Results
• The ability to change convergence average peak velocity was
significantly greater (p < 0.03) in presbyopic PALs adapters
compared to presbyopic PALs non-adapters.
• The rate of phoria adaptation and vergence facility were
significantly greater (p < 0.03) in incipient presbyopic PALs
adapters compared to incipient presbyopic PALs non-adapters.
• Vergence facility and the rate of phoria adaptation may have
potential clinical utility in differentiating which patients may
adapt to PALs and which ones will have more difficulty.

54. Rate of phoria adaptation in PALs acceptability
• The non-adapters to PALs had a reduced ability to adapt to a
visual target in near space compared to adapters of PALs.
• Therefore, during the initial trial period of wearing PALs, the
ability to quickly adapt to visual targets at different spaces (close
to a subject compared to far away) may be an important trait in
presbyopes adapting to PALs
Conclusion

55. • Also the adapters to PALs demonstrated a significant increase in
the change in the magnitude of phoria adaptation compared to
non-adapters to PALs.
• Decreases in the change of the magnitude of phoria during phoria
adaptation is one of the potential causes of asthenopia or visual
complaints.
• Visual complaints that are commonly experienced by non-
adapters to PALs may be associated with a decrease in the rate of
phoria adaptation and perhaps the reduced ability to change the
magnitude of phoria.

58. • Significant differences in vergence facility performance were
observed in visually symptomatic and non-symptomatic non-
presbyopic group using prisms of 3Δ base-in and 12Δ base-out
while fixating on a near target (40 cm).
• The threshold value of 15 cycles per minutes (cpm) yielded
highest sensitivity (75%) and specificity (85%) for correctly
identifying symptomatic and non-symptomatic subjects.
Vergence facility and PALs acceptability

59. • McDaniel and Fogt reported that phoria changes before and after
vergence facility measurements and that vergence facility may be
affected by phoria adaptation.
• The vergence facility was highly correlated with the rate of phoria
adaptation and moderately correlated with the change in
magnitude of phoria adaptation.
• Thus, vergence facility may reflect the adaptability of both
vergence and phoria systems.

61. Other Factors influencing PAL Acceptance
• Gambra and colleagues results support that the presence or
absence of high-order aberrations caused by PALs alter the
accommodative response and the fluctuations of
accommodation where the presence of larger amounts of high-
order aberrations produce accommodative lag.
• Sawides and colleagues support that high order aberrations and
astigmatism including the distortion produced by the
astigmatism may also influence the adaptation to PALs.
• In addition, the PALs design can introduce undesirable
astigmatism within the periphery that will degrade vision and
negatively impact PALs adaptation

62. • The ability to change convergence peak velocity had the
greatest sensitivity and specificity compared to the other
parameters.
• However, vergence facility has potential for use in the clinic
because of its ease of administration, the amount of time
required to conduct the test, and the cost of required
instrumentation.

63. Patient satisfactory survey
• The success of a progressive-lens fitting depends on a
chain of actions that can each be a source of inaccuracy.
• In general, the expression of dissatisfaction is, in fact,
the result of their inability to adjust to the lenses. This
notion remains very generic and does not help to
explain the real causes of the wearer’s problems.

64. Figure : Overall satisfaction of those who responded to the satisfaction survey.

65. Figure : Satisfaction rate as a function of the addition prescribed.

66. Figure : Ametropia and addition distribution of those who came back to the store.

67. Figure : Main reasons for returns.

68. Analysis of a progressive addition lens
population
• Wittenberg (1 978) has noted that patients wearing a correction
with a high cylinder may be more likely to succeed with PALs.
• Patients with a high cylindrical correction have a poorer
standard of vision and are therefore less able to appreciate the
deterioration in vision due to the introduction of PALs.
• Alternatively, it might be suggested that patients with high
astigmatic corrections are better able to adapt to PALs because
of their prior experience of wearing highly astigmatic sphero-
cylindrical corrections.

69. • The ranking system, used to determine the patient
preference for PALs, showed that both adapters and non-
adapters found the reading portion to be the most
unsatisfactory area.
• Patient dissatisfaction may be due to the relatively greater
usage of the reading portion compared to other portion.
• Furthermore, whilst the reading portion may be spherical
along the umbilical line, the lateral areas on either side of
this meridian are often highly astigmatic.

70. • It is suggested by some manufacturers and dispensers that
the reading addition prescribed for a PAL wearer should be
an extra +0.25 DS more positive than would otherwise be
prescribed.

71. Satisfaction level of PAL wearers
• The majority of PALs wearers have the acceptance rate at 90% or
more due to the comfortability and the quality of vision that PALs
provided (Hons, 2008).
• The high acceptance rate of PALs can be due to the elimination of
imaginary lines and jumping images in which reduce the sudden
change in the prismatic and increase the comfortability of the
wearers (Walsh, 2001).
• Odjimogho (2004) surveyed 106 PALs wearers aged between 37 to
66 years old. 69.8% of patients have a high rate of comfortability
with their PALs.

72. • A previous study by Han et al., 2011, has compared patients’
satisfaction with progressive lenses with other types of presbyopic
correction. They revealed out that most the subjects involved were
satisfied with progressive lenses rather than other type of lenses.
• Cosmetically, PALs offer a desirable additional power without the
lines and ledges that fundamentally „blend‟ the transition between
distance and near zones (Meister & Fisher, 2008)
• Ninety-two percent of patients involved in the study by Boroyan et
al. (1995) preferred PALs as compared to a lined multifocal due to
the cosmetic purposes (Lynn, 1998).

73. • It represented the overlapping of multiple individual focal
points, where each have their own range of clear vision, hence
providing a single, broad expanse of clear vision from infinity
to near distance (Gispets, Pujol, & Vilaseca, 2011).
• Clear vision is possible to some extent at all distances and
certainly increased the quality of vision (Walsh, 2001).
• According to Gime, 2008, although bifocal lenses were more
appreciated for their near field of view, progressive lenses have
had a very high success (97%) since the 1970s (Gime, 2008).

74. • A previous study by Spaulding (1981), involving 48
multifocal candidates and their preferences of multifocal
lens design. 52% preferred PALs lenses as compared to
bifocal design (48%) (Lynn, 1998).
• According to (Chu, 2010), one study demonstrated that up
to 92% of previous bifocal wearers preferred progressive
addition lenses (PALs) when given a choice between PALs
and bifocal lenses following a trial of PALs.

75. • The success of the visual performances with PAL spectacles
have correlation with the optics of the lenses, the fit of the
frame and the position wear including eyes and head
movement for visual tasks at a different viewing distance and
the individual characteristics of the patient.
• The adaptation and satisfaction of PALs can be hampered by
The restricted optical zones; This makes reading at both
intermediate and near distances a problem (Spencer &
Ciuffreda, 2002) and also lead to the increment frequency of the
compensatory head movement to get clear vision.
The prismatic effect of the lateral sides of PALs

76. PALs wearers may be aware of the lateral image blur that can
adversely affect the success of the adaptation process (Mok,
Chung, & Kwok, 2011).
Most of the PALs wearers complained of vertigo and dizziness
when changing gaze horizontally (Suemaru, Hasebe, & Ohtsuki,
2008).
PALs wearers were also needed to view the appropriate part of
the lens to obtained clear vision depending on the distance of
the object.
 The progressive lens costs more than other types of correction
lenses for presbyopia.

77. • The different viewing area or different tasks to be a major factor
that affects the satisfaction level as people seek for best correction
lenses to help in improving their visual acuity and improving their
quality of life.
• Measuring the variances at different viewing areas has proven to
affect the visual task performance (J. Sheedy, Hardy, & Hayes,
2006).
• Hence, patients should be aware that, different zones‟ widths and
areas across the lens were designed to satisfy their visual
performances.
Quality of Vision and Total Satisfaction of
PALs wearers

78. Quality of Vision and Total Satisfaction of
PALs wearers
Figure 3.1 Mean quality of vision at the
different viewing area.

79. • The result shows that the level of visual satisfaction was highest at
the intermediate as compared to the distance and the near viewing.
(Satisfaction Level of Progressive Additional Lens (PALs) Wearers ,Nur Aresya Ahmad
Najmee, Noor Halilah Buari, Rabiatun Mujari, Muhammad Irwan Rahman ,Optometry,
Faculty of Health Sciences, Universiti Teknologi MARA, 42300 Bandar Puncak Alam,
Selangor, Malaysia ,14-16 Oct 2017)
• During reading, the eye does not move in an orderly manner. They
pause, move backwards and jump from one point to another;
hence require a high level of accommodation (Batemanazan et al.,
2014).
• These findings support the prediction by the study where reading
involving size print would require the use of the clearest portion of
the lens and the clarity of vision is ideal at the centre of the near
zone (Lynn, 1998).
• However, this was contradicted by the study done by Gime,
(2008), the distance vision tasks have higher satisfaction, but for
near vision, the task received the lowest score.

80. • During driving, by viewing an object at a distance paired
with vision disturbance; peripheral blur, unwanted
astigmatism and distortion.
• A study conducted by Ellison, (2012) justified the same
effect on PALs wearers. Activities such as driving or walking
by using progressive additional lens cause the vision to
appear to oscillate at the sides.
• The peripheral astigmatism can change the power along the
vertex line of the PALs progression. Thus wearers may
experience astigmatism with the occurrence of blur when
the eye moves toward the other different viewing areas.

81. Symptoms Reported and Total Satisfaction
of PALs wearers
Figure 3.2 Mean symptoms reported associated with PALs.

82. • The highest reported symptoms related to the use of PALs lenses
were blurry vision with a mean of 7.07±2.60, followed by eye
strain (7.27±2.55), dizziness (7.33±2.86) and headache
(7.47±2.93).( Nur Aresya et al.,2017)
• Poor adaptation, changes of power profile in term of
magnification, astigmatism or aberration along the PALs lines
can be the main causes of blurry vision.
• A similar result is obtained from the quality of vision at distance
viewing which shows the lowest satisfaction.
• This likely due to the optical design of the PALs as progressive
additional lens require gradual changes of distance to near area
which caused unwanted distortion through the lower lens
periphery (Chu, 2010).

83. Sample of questionnaire for
satisfaction level of PAL wearers

84. • The free form design and PAL with wavefront technology is
better than conventional design PALs .
• The width of Distance, Intermediate and Near zone should
consider in new design of PAL according to individual’s visual
need.
• In PAL, 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.
• The lens design of the intermediate zone must be carefully
considered in new PAL lens designs with the intent of
producing more efficient and comfortable reading, approaching
that found with the SVL.
Discussion

85. • PAL wearers may also notice the perceptual phenomenon of
“swim” due to non uniform and asymmetric magnification for the
optical regions adjacent to the intermediate lens zone.
• Thus, wearers may need time to adapt to these motor and
perceptual components to optimize use of the PALs and become
symptom free.
• The ability to modify the vergence and phoria systems is
significantly different between presbyopes who could not adapt to
PALs and presbyopes who have successfully adapted to PALs and
wear them regularly.
• For computer users special computer vision PAL is preferable over
general purpose PAL.

86. • The high acceptance rate of PALs can be due to quality of vision,
cosmetic purpose, no image jump, the elimination of imaginary
lines and jumping images and increased comfortability, broad
expanse of clear vision from infinity to near distance and replace
the need to have multiple pairs of glasses for multiple function.
• Where as the symptoms associated with PAL like blurry vision,
dizziness, reduced depth perception on walking, headache,
peripheral distortion etc decreases the satisfaction level of PAL
wearers.

87. Sources of dissatisfaction of PAL wearers
Distortion;
• The power progression in PAL creates regions of aberration results in
poor visual resolution
• As the lenses combine a range of powers in a single surface there
occurs geometric distortions to the visual field, which increase with
the addition power
Cost:
• significantly higher price than bifocal and single vision reading
spectacles
Requires a short period of adaptation
Fitting:
• Incorrect specification of the fitting location causes narrow fields of
view, clear vision in one eye only, on-axis blur, and the need to adopt
uncomfortable head positions

88. Fitting and Verification of PAL
• Back vertex distance - Minimum
• Pantoscopic tilt - 10 to 12 degrees
• Facial wrap - It must follow the line of the face
• Level of the frame - Frame should sit squarely on the face
• Temple length - Optimum length to minimize sliding
• Nosepad - Adjustable

89. Conclusion
• Despite limitation, progressive additional lenses are the best
option for the presbyopic population.
• Even though it had been introduced to the public many years
ago; approximately 40 years, the improvement of the PALs design
are consistently released as there was always a high demand for
needs of the better understanding towards its progressive surface
(Pope, 2000).
• The eye-care practitioners should aware of the PALs wearers
‘priority and requirements’ in selecting the appropriate lens
design that matches with the tasks required.
• Additionally, by time to time, due to advance in technology, there
will be some improvement in PALs designs, potentially reducing
the possibility of symptoms, hence increasing satisfaction level
among PALs wearers in the future.

90. To Remember…
• Identify patient’s requirements & expectations
• Highlight the features of Progressive lenses
• Explain the limitations

91. 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
• CET articles
• Internet