1. science
2. physics
3. optics

MODULE 5
Certificate Course In Ophthalmic Dispensing Leading To
Certified Dispensing Optician (CDO)
Pre-Adjust the Frame
Effect of Pantoscopic Tilt
10o Pantoscopic Tilt
Carl Zeiss Vision
Measurement Tools
Measure the Distance Pds
No Pantoscopic Tilt
Measure the Fitting Heights
Verify cut out
------------------R
Effect of Incorrect PD
Measurements
PD Error
Verification by Lensometer
Progressive fitting layout card
Control of coma-like
aberration in distance vision
(Varilux Pysio )
R
a = distance portion
b = intermediate zone
c = near zone
d = distortion
a
d
b
d
c
Improvements brought by
Varilux Panamic for
experienced presbyopes.
Manufacturing Of
Progressivse Lens
Varilux Panamic
Classic Progressive
b) Binocular vision
Wavefront Management
System™
Slumping process
b) Slumping a glass blank (forming)
a) ceramic mould
Certificate Course In Ophthalmic Dispensing Leading To
Certified Dispensing Optician (CDO)
MODULE V
(Study Notes)
COMPILED BY
MR. YOGESH KOTHARI
MS. KOMAL CHAURASIA GUPTA
C
2006 All rights reserved with Yogesh Kothari
For Educational purpose only not for commercial use. This is a compilation of notes, diagrams
as study material from various sources, notes from the institution and Web. The copyright if any,
remains with the respective owner of the copyright of respective material. We hold the copyright
only for the concept & presentation.
A
References
1) Troy E. Fannin Clinical Optics : 2nd Edition
2) Jalie M. Ophthalmic Lenses and Dispensing (2003) : 2nd Edition.
3) L.S. Sasieni. The Principal and Practice of Optical Dispensing and Fitting 3rd Edition
4) Clifford W. Brooks, System for Ophthalmic Dispensing, 5th Edition.
5) Duke Elders Practice of Refraction 10th Edition.
6) Personal Study Notes.
B
I.S.D.T.- CDO
Module 5 : Progressive Addition Lenses
detract from the appearance of the lenses.
These all limitations are eliminated by progressive
addition lenses, which becomes very popular from past
4.
few years. Indeed, in their country of origin, France,
progressive lenses have become the first choice of
multifocal design for the correction of presbyopia.
•
Single vision provides a vision at predefined single
distance i.e. either for distant object or for reading
•
Bifocal : to overcome shortcoming of using different
sets of single vision lenses for different distances
the next step invented that contains two different
powers for two different predefined distances i.e.
single lens with two parts, one for reading other for
distant viewing
•
Trifocal : the lens specially devised for specific
professions who needs viewing at different distances
simultaneously. This type defines three vision areas
namely distant, reading and intermediate
•
All these lenses have limitations in terms of viewing
distances those are predefined by the user need
•
To overcome this limitation the new generation of
lenses were developed. This lens ideally overcomes
all the above limitations concerning with viewing.
Provides vision or range of vision from closest
distance i.e. reading to the far vision uniformly without
compromising any of the areas of vision.
•
These lenses claims to provide natural vision like an
young individual.
•
These lenses are called as Varifocal/ Multifocal/
Progressive lenses.
•
Progressive or varifocal
Why progressive?
5.
Progressive lens
Provide a smooth transition from distance correction
to near correction, eliminating segment lines and
allowing the viewing of all intermediate distances
(invisible series of horizontal curves joins distance
vision, intermediate vision and near vision).
2
I.S.D.T.- CDO
Module 5 : Progressive Addition Lenses
12.
The basic principle is followed in the construction of all
progressive addition lenses as shown in this diagram.
Basic principle in the
construction
of progressive surface
You can see the distinct portion upper portion with longer
radious and lower is with shorter Radius.
The upper portion consist of distance power and lower
with near power. The zone that connects these two is
madeup by insertin on Aspheric surface that continuous
change of correct upper potion of zone has radious closer
to distance portion level portion has radious closer to
near vision portion. The aspheric surface matches the
radious at both end . So no lines are seen power
increases gradually towards near portion reaches to
maintain at addition.
13. Progressive Addition Lenses
Advantages
– No visible segments or lines of
demarcation
• More appealing cosmetically
– Clear vision at all distances
• There is a continuous range of vision
from distance to near
– No unwanted differential image
displacement or jump
Compared with single vision and bifocal lenses,
progressive lenses offer presbyope the following
advantages :
• Continuous vision from distance to near : single
vision lenses offer a range of clear vision in the near
area only whereas bifocal designs, with their abrupt
change in power, create two ranges, one for distance
and one for near vision.
• Comfortable vision for all intermediate distances
(50 cm to 1.5 m) since the progressive lens is the only
design which has zones specifically designed for
these distances. In the early stages of presbyopia
(additions less than 1.50 D), the wearers of single
vision and bifocal lenses may still obtain clear vision at
these distances. A low reading addition, together with
their remaining amplitude of accommodation, enables
them to see clearly over this range. On the other hand,
in later stages of presbyopia (additions over 2.00 D),
clear intermediate vision is no longer possible since
the remaining amplitude of accommodation is too
little, and the reading addition too great, to provide
clear vision at these distances. Only progressive
lenses allowcomfortable vision at all intermediate
distances.
•
Continuous support for accommodation adapted
for all distances : with a progressive lens the eye can
find some region of the progression zone where the
power is correct for the viewing distance. In the case of
a single vision reading lens, vision is possible only for
near vision. With a bifocal lens the eye must increase
and then relax its accommodative effort as it passes
through the intermediate range.
I.S.D.T.- CDO
5
Module 5 : Progressive Addition Lenses
267.
Internal PALs
Internal PALs
--------------– --------------------------------- ----------------- -----------
Internal PAL
Field of View
Significantly
expanded
External PAL
Fig.1: Moving progressive curves from the front surface (in red)
to the back surface (in green) broadens the field of view
Let's re-examine the four inherent problems of external
PALs and see how they are affected when the
progressive curves are positioned on the backside, as in
an internal progressive.
1. Differing magnification throughout the lens.
Magnification differences between various areas of the
lens are greatly reduced. This reduction occurs because
variations in the front surface are now eliminated, as it
becomes a spherical surface. Moving the progressive
curves to the backside produces considerable reduction
in size distortion. Another benefit is that moving the
progressive surface closer to the eye also reduces the
skew distortion common to external PALs . As a result,
patients experience less swaying and swimming
sensation.
2. Restricted visual field. Moving progressive curves to
the backside produces a very significant expansion of the
visual fields for all distances. Another factor affecting field
of vision comes from the fact that back curves are atoric
or aspheric (depending whether there is cylinder in the
Rx). The internal progressive manufacturer has
designed aspheric compensation that is Rx specific,
meaning each curve has been aspherized to the patient's
exact correction. Aspherizing curves creates a flatter lens
positioned closer to the eyes, and this also expands the
fields of vision. Expansion of the visual fields benefits all
areas of view: distance, intermediate, and near.
3. Compromised optics. In this regard, an internal PAL
produces the maximum efficiency because, unlike
external PALs, no compromise is required in selecting
base curves. Both surfaces of the lens have been
optimized to the patient's specific correction, and the
posterior surfaces are either aspheric or atoric
(depending on whether there is cylinder in the
correction), providing the most exacting acuity possible.
4. Off-center astigmatism and power errors that
increase with refractive index. In this problem area,
changing to an internal design produces total control of
off-center astigmatism and power errors common to
external PALs. In addition, any small amounts of offcenter astigmatism and power errors that remain are not
increased when higher index materials are used. This
consistency, regardless of index, results because there is
no lens material between the progressive curves and the
wearer's eyes. The near correction experienced by
wearers is consistent and identical to that prescribed by
the refractionist. There is accurate power throughout an
expanded reading area. Unwanted cylinder power to the
sides of the intermediate area (progressive channel) is
controlled and greatly reduced. In the distance portion,
wearers experience a remarkably wide, distortion-free
view. There has been marked improvement throughout
the entire lens. To provide a clearer idea of what this
means to wearers, in a prescription calling for plano
distance with a +3.00 add, wearers will experience 30
I.S.D.T.- CDO
123
Module 5 : Progressive Addition Lenses
percent less distortion coupled with a 20 percent wider
visual field.
With the powerful computing capability now available
from modern computers, designing a comprehensive
internal progressive with an Rx-specific back surface
map has become possible. This left two major hurdles.
First, there was the difficulty of transferring computer
designs to the back of the lens. Once that was
accomplished, there was the complexity of
manufacturing a progressive lens specific to each
patient's prescription. Equipment to produce these
268. Fitting Internal Progressives
• Depending on the brand
• Internal PALs can be fitted as low as
16mm, useful for today's shallow frame
styles
• Use the manufacturer's cut-out chart to
ensure that the lens blank size will fit the
frame selected by the patient.
sophisticated aspheric/ atoric surfaces only recently
became available, and creating this complex surface
with a mirror-like finish is beyond the capability of
conventional laboratory equipment. The internal
progressive manufacturer has developed such
equipment and can fill individual prescriptions for their
distributor labs.
Fitting Internal Progressives
Practitioners now have the ability to take a quantum
leap forward in fitting progressive patients. Fortunately,
fitting this complicated technology remains relatively
simple. Like all PALs, PDs for internal PALs should be
determined monocularly by using an electronic
pupilometer. The fitting cross (also known as the eye
point) is positioned exactly in the center of the pupil. The
lab needs to know the frame PD, the vertical dimension of
the frame ("B" measurement), and height of the fitting
cross. When the correction is plus, Seiko Optical
stresses that fitters must also provide the ES
measurement, which is the distance from the fitting cross
mark to the furthest point of the lens shape. This ensures
a lens with the thinnest possible edges.
Depending on the brand used, internal PALs can be fitted
as low as 16mm, useful for today's shallow frame styles.
Use the manufacturer's cut-out chart to ensure that the
lens blank size will fit the frame selected by the patient.
Due to the aspheric compensation in the internal
progressive, eye power perception may vary from the
actual lensometer reading in the near portion of the lens.
Distance power is verified the same as on an external
progressive, and the add power can be verified by
checking the engraved markings on the lens.
Lenses with this advanced internal progressive
technology, combined with Rx-specific aspheric/atoric
curves for all portions of the lens, are more expensive
than conventional PALs. When the benefits of these
lenses are properly explained to the patient, there should
be a substantial number who will want the finest available
progressive technology for their new glasses.
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I.S.D.T.- CDO
Module 5 : Progressive Addition Lenses
269. Points to remember about
succesful progressive
lens Dispensing
• Understand patient needs
• Accurate refraction
• Right frame selection
• Accurate measurement
• Appropriate selection of lens design
• Patient counseling about adaptation, wear,
•
limitations etc.
Proper fitting
I.S.D.T.- CDO
125
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