MODULE 5

Certified Dispensing Optician (CDO)Certificate Course In Ophthalmic Dispensing Leading To

Carl Zeiss Vision Measurement Tools

Measure the Distance Pds

Measure the Fitting Heights

Verify cut out

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R

PD Error

Effect of Incorrect PD Measurements

Verification by Lensometer

Pre-Adjust the Frame Effect of Pantoscopic Tilt

o10 Pantoscopic Tilt No Pantoscopic Tilt

a

b

c

d

distance portion

intermediate zone

near zone

distortion

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=

=

=

a

b

c

d d

Progressive fitting layout card Control of coma-like

aberration in distance vision

(Varilux Pysio )R

b) Binocular vision

Varilux Panamic Classic Progressive

Improvements brought by Varilux Panamic for

experienced presbyopes.

Manufacturing Of Progressivse Lens

Wavefront Management System™

Slumping process

a) ceramic mould

b) Slumping a glass blank (forming)

MODULE V

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.

C 2006 All rights reserved with Yogesh Kothari

COMPILED BY

MR. YOGESH KOTHARI

MS. KOMAL CHAURASIA GUPTA

Certified Dispensing Optician (CDO)Certificate Course In Ophthalmic Dispensing Leading To

(Study Notes)

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.

I.S.D.T.- CDO B

2

4.

detract from the appearance of the lenses.

These all limitations are eliminated by progressive

addition lenses, which becomes very popular from past

few years. Indeed, in their country of origin, France,

progressive lenses have become the first choice of

multifocal design for the correction of presbyopia.

Why progressive?

•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.

Single vision provides a vision at predefined single

5. Progressive lens • Progressive or varifocal

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).

Module 5 : Progressive Addition Lenses

I.S.D.T.- CDO

5

12. Basic principle in the construction

of progressive surface

The basic principle is followed in the construction of all

progressive addition lenses as shown in this diagram.

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.

Module 5 : Progressive Addition Lenses

I.S.D.T.- CDO

I.S.D.T.- CDO

Internal PALs 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 off-center 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

Module 5 : Progressive Addition Lenses

267. Internal PALs

Fig.1: Moving progressive curves from the front surface (in red) to the back surface (in green) broadens the field of view

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Field of ViewSignificantly

expanded

Internal PAL

External PAL

123

I.S.D.T.- CDO

268.

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

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

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.

••••

••

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.

Module 5 : Progressive Addition Lenses

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I.S.D.T.- CDO

269. Points to remember about succesful progressive

lens DispensingUnderstand patient needsAccurate refractionRight frame selectionAccurate measurementAppropriate selection of lens designPatient counseling about adaptation, wear,limitations etc.Proper fitting

••••••

•

Module 5 : Progressive Addition Lenses

125

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