UNIT 2: Progressive Addition Lenses Flashcards
Why did PAL’s take so long?
- Simple to conceive but challenging to produce
- Machinery capable of creating non- regular
surfaces had to be created.
Creating Progressive Power
- Increased curvature creates more plus power (
with a stable index) - Aspheric curvatures needed to create plus
power on PAL’s - Increasing power creates surface astigmatism
How is surface astigmatism created?
- Due to the changing surface curvature.
- It is an unwanted by- product of aspheric
curvature.
What does surface astigmatism do?
It blurs vision just as if the wearer were looking through incorrectly prescribed cylinder.
Hard Design PAL’s
- Concentrates the astigmatic error into smaller
areas of the lens surface. - Expands the areas of perfectly clear vision.
- Higher levels of blur and distortion.
List 4 characteristics hard PAL’s exhibit
- Wider distance zones
- Wider near zones
- Shorter, narrower progressive corridors
- Higher, more rapidly increasing levels of
astigmatic error
In general, harder PAL designs:
- Provide wider fields of view
- Require less head and eye movement
- Provide more swim and blur
In general, softer PAL designs:
- Provide reduced levels of astigmatism and
swim - Limit the size of the zones of clear vision
- Require more head and eye movement
Softer Design PAL’s
- Spreads astigmatic error across larger areas of
the lens surface. - Reduces the overall magnitude of blur
- Narrows clear vision zones
- Astigmatic error may encroach well into the
distance zone.
List 4 characteristics soft PAL’s exhibit
- Narrower distance zones
- Narrower near zones
- Longer, wider progressive corridors
- Lower, more slowly increasing levels of
astigmatic error.
When was the concept of PAL’s patented?
1907
What was the first progressive lens marketed in the world?
Varilux by Essilor
When was Varilux marketed to the world?
1956
Who designed Varilux?
Bernard Maitenaz
What material is Varilux made in?
Glass
What design was used in the upper half of Varilux and why?
Spherical design used to create a large, clear distance zone with no surface astigmatism.
FILL IN THE BLANK
All progressive power is centered in a ________ intermediate zone in a Varilux lens.
12mm
FILL IN THE BLANK
Power in the lower portion resulted in a ______ wide stable and essentially spherical zone.
22mm
What type of design is Varilux considered?
Hard design
What was the first US PAL’s?
Omnifocal
Who designed Ominfocal?
David Volk and Joseph Weinberg
When was Omnifocal designed?
1961
TRUE OR FALSE
Omnifocal was sold by Univis Lens Company in 1973.
False: 1965
What material is Omnifocal made in?
Glass only
In omnifocal lenses, is the decreased radius of curvature vertical or horizontal?
Vertical
TRUE OR FALSE
In Omnifocal, it has a narrowing corridor design from top to bottom.
True
How much distance is between the distance and near centers of a Omnifocal lens?
25mm
What kind of progressive design is Omnifocal lenses?
Soft Design
When was Varilux updated to Varilux 2?
1972
Varilux 2
- Released in both glass and plastic materials.
- Lens completely aspheric
- Soft design
- Tilted corridor in its design
- Creates true right and left lens blanks
- Eyes experience equal power changes as they
scan around the lenses binocularly.
Who introduce UltraVue?
American Optical
When was UltraVue introduced?
- UltraVue 25 in 1975
- UltraVue 28 in 1979
UltraVue
- Had a large, wide, and clear distance zone free
from astigmatism. - Progressive power within 10-12mm in the
intermediate zone. - Wide essentially spherical near zone.
- Had high levels of surface astigmatism
peripherally and closely positioned to the
corridor.
In UltraVue, was the corridor tilted?
The corridor is NOT tilted
How was UltraVue made?
- Using one lens blank rotated nasally right or left 10 degrees by the lab to create the appropriate lens.
- Creating approximately a 2.5mm near zone inset.
What does the single blank design of UltraVue present?
Unequal powers to the eyes scanning binocularly.
Varilux Infinity
- Introduced multi-design
- 12 Designs: one for each add power
(+0.75D to +3.50D) - Low add = soft design with a long corridor
Asymmetrical Design
- Introduced by SOLA Optical (1987) with the
SOLA XL lens - Distributed unequal amounts of surface
astigmatism on either side of the umbilical
midline. - Placed more surface astigmatism in the lower
nasal portion than in the temporal and
peripheral portions. - Concept = surface astigmatism in the lower
nasal portions of the lens is relatively
unnoticed. - Also aided in reducing the overall amount of
surface astigmatism in the lens.
Various Segment Inset
- As the eye tracks down the progressive
corridor into the near zone, it encounters
prismatic effect. - Pulls the eye off the midline.
- Adjust the location of the near zone to
compensate for prismatic effect.
In short corridor progressives, what corridor length keeps surface astigmatism low?
Long ; some lenses had corridors as long as 25mm
In short corridor progressives, what frame size had shallower B measurements?
Small ; Longer corridor lenses didn’t fit (The near zone was cutoff in edging)
AO Compact
- First short corridor lens
- By American Optical
- 15mm min recommended fitting height
- Ideal for shorter/ smaller/ shallower frame
styles. - Still on the market
- Nearly every major lens manufacturer offers
one or more short corridor progressive
designs.
What is optical ray tracing used to determine?
How an object will image on the film in a camera.
What can ray tracing tell a designer?
- Illustrate areas of blue, distortion and
magnification. - Illustrate the amount and the axis of surface
astigmatism at various points of the lens. - Illustrate lens aberrations and distortion, mag
and other optical focusing characteristics.
Where does vision occur?
In the visual cortex of the brain.
Who was TruVision Technica designed by?
- American Optical ( 1988 )
TruVision Technica was designed to provide what?
- Width of lens intermediate and near viewing
- Small, usable distance window for viewing
objects across the room or on the wall.
When was Hoyalux TACT introduced?
1998
What does Hoyalux TACT offer?
- Wide intermediate and near zones with limited
distance vision. - 2 fitting heights:
1) EP40 - Standard viewing position
- Wide near vision, limited elsewhere
- 40% of the add power at the fitting cross
location.
2) EP60 - Near vision position
- No distance area but a good
intermediate and very wide near zone.
- 60% of the add power at the fitting cross.
Near Environment Lenses
- Computer lenses
- No distance zone
- Progressive power more gradual
- Less aberrations, distortion, and blur.
- Not meant to replace progressives
What is Rodenstock Impression ILT?
- One of the first individualized progressives
- 2001
- Aspheric / atoric back surface for this front surface PAL’s
Varilux Ipseo
- Individualized progressive
- Takes into account the patients visual behavior
to create a progressive that’s individualized. - Uses The Vision Print System
Vision Print System
- Measures head and eye movement of patient
- Translates into visual behaviors fingerprint
- Data used for customization of lenses
Two ways to create direct to surface application?
1) Making molds
2) Cutting the surface directly on the lens blank
Mold Making
- Traditional progressives are cast
- Monomer takes the shape of the two molds
What are traditional progressive molds made of?
Slumping
Slumping
- The glass mold material is heated and takes
the shape of the die use. - Two molding processes are used:
1) One making the mold
2) Another when making the lens
Direct to Surface Mold Making
- Mold is created by direct surfacing
- Accuracy is improved: approximately 0.01D
( conventional molding accurate to 0.06D )
Direct to Surface Lenses
- Created when one surface is directly surfaced
to direct to surface generation. - Direct-to-surface PAL’s are produced several
ways.
- Generate the lens distance power on the
backside.
( for a front surface progressive design ) - Direct-to-surface cuts the progressive surface
onto the lens. - Both sides surfaced using direct to surface
processing.
Vertical Alignment
- Sit across from the patient so that you are
at the same eye level.
TRUE OR FALSE
Sighting upwards ( sitting too low ) gives lower segment height measurements.
TRUE
TRUE OR FALSE
Sighting downward ( sitting too high ) gives lower readings.
FALSE: Gives higher readings
Horizontal Alignment
- Be sure that the midline of your face is
aligned with the midline of the patient’s
face. - If you are positioned to the right or left, the
markings placed on the lenses will be
incorrectly positioned by equal amounts to
the right or left.
Fitting Height Measurement
- Seated in proper facial alignment, have the
patient gaze into your left eye. - Measure from the inside of the frame’s
bezel ( frame groove ) to the center of the
patient’s pupil. - For frames with demo lenses, you can
simply mark the lenses at this location. - Without moving your head, have the
patient look into your right eye and take
the second measurement. - Again, without moving your head, repeat
both measurements to ensure accuracy.
What are traditional fitting measurements limited by?
- Accuracy
- Precision
- Reliability
- Consistency
What factor is accuracy affected by and what is it?
Parallax Error: The apparent displacement of the wearer’s pupil at the plane of the spectacle lens as the dispenser changes position.
What is precision limited by?
The measurement tool
What does the pupilometer measure?
Corneal reflex
Corneal Reflex
- Reflex is independent of the dilative state
- Reflex is easy to locate/measure
- Eye’s optical axis falls close to the reflex
Fitting Height
The distance between the center pupil & the lowest edge of the lens.
Optimal Lens Tilt
- Lens tilt influences the optics
- Most PAL’s are designed for about 8
degrees vertical tilt. - Wrap brings the periphery of the lens
closer.
Modern Measurements
- Customized PAL’s may require additional
measurements.- As Worn:
- Tilt, Wrap, Vertex
- Head Cape, ERCd
- Personal Visual Habits:
- Head/ Eye Movement
- As Worn:
FILL IN THE BLANK
_____________ progressive lens base curves are calculated on averages, and if a patient’s distinct requirements fall beyond this range, vision is ________________.
1) Traditional
2) Compromised
Computerized Measurement Systems
- Pupil Meter & Pupilometer Pro for Ipad
- Optikam
- Zeiss: iTerminal
- Essilor: Visioffice
- Hoya: Spectangle
The Centration Module
- Anatomically adjusted frame
- Patient stands or sits in relaxed, habitual
posture. - Unique, patented speckle image causes
patients eyes to relax for accurate distance
PD measurement. - A precision digital camera captures front
and side images of the patient in his or her
chosen frame. - Sophisticated software makes all key
measurements to an accuracy of 0.1mm.
Lens centration and fitting
- i.Terminal incorporates unique, patented
laser speckle target system. - Ensures that the wearer maintains proper
distance fixation while the photo is
captured, and that the wearer is properly
centered in front of the system. - Automatically compensates for any
accidental head rotation.
Lens centration and fitting
- i.Terminal incorporates unique, patented
laser speckle target system. - Ensures that the wearer maintains proper
distance fixation while the photo is
captured, and that the wearer is properly
centered in front of the system. - Automatically compensates for any
accidental head rotation.
Carl Zeiss Vision
- Zeiss Individual
- Additional customization if iTerminal is
used. - Measures:
- Monocular P.D.
- Fitting Height
- Vertex Distance
- Frame Wrap
- Pantoscopic Tilt
The Consultation Module
- High resolution photo images allow patient
to see clearly how they will look in their
chosen frames. - Images can then be enhanced to show the
appearance and effects of:- AR Coating
- Photochromic
- Fashion Tints
Eye Rotation Center
- Point through which optical axis always
passes. - Determines optical projection on the retina.
What is Head Cape?
- The measurement of the natural resting
position of the head. - Each 2 degree of head cape results in 1 mm
horizontal shift. - Studies show the average head cape is
approximately 1.5 degree.
Progressive Lens Markings
- Distance verification circle
- Near verification circle
- Fitting cross
- Prism reference point ( PRP )
- Datum line ( 180 degree line )
How is fitting height verified?
- Using a mm ruler
- Lens cut out chart
