MADE BY : SWATI PANARA
FROM : BHARTIMAIYA
COLLEGE OF OPTOMETRY
2nd YEAR 3rd SEMESTER
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• A – NOT
• SPHERIC - SPHERICAL
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• In 1909 – Zeiss – Katral lenses.
• In 1958– David Volk – Volk conoid lenses.
• In 1970s – Robert Welsh – Welsh 4 drop
• 1976 – Davis and Fernald – patented a
series of aspheric lenses .
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• In 1980 – Whitney , Reilly and Young
patented Fulvue aspheric blended
Lenticular lenses .
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• The literal meaning of “aspheric” is simply
“not spherical”, which means cylinder
surfaces or toroidal surfaces used for
• In terms of “lens designing” the term
“aspherical” usually refers to a surface that
is rotationally symmetrical, but at the same
time not spherical.
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• A change in curvature is noticed over the
lens surface, rather than constant curvature
like a spherical surface.
• The change is the same in all direction or
meridians of the lens.
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• The “asphericity” is achieved by flattening
the periphery of the front surface in plus
lens and by steepening the periphery of the
front surface in minus lens and/or by
flattening the periphery of the back surface
to reduce the edge thickness.
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• THE PRINCIPAL USE OF ASPHERIC
LENS DESIGN IS THE REDUCTION OR
ELIMINATION OF OPTICAL
ABERRATIONS PRODUCED BY
LOOKING THROUGH AN
OPHTHALMIC LENS OBLIQUELY.
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• Four types of conic section:
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It‟s formed by horizontal plane
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Ellipse conic section
It‟s formed by angle plane through cone
don‟t intersect the base of cone.
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Parabola conic section
Intersection of cone with plane having
one side parallel to the side of cone.
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Hyperbola conic section
Intersection by plane that makes of cone
than the side of cone make with its base.
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• Unfortunately several lens aberrations affect
the quality of peripheral vision through a
• Oblique astigmatism is the principal lens
aberration that is considered to be the most
serious defect in designing the ophthalmic
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• When the rays of light strike the periphery
of the lens obliquely, two focal lines are
produced from each single object point.
• The dioptric difference between these two
focal lines is known as the astigmatic error
of the lens.
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• CHOOSING A FLATTER BASE CURVE
WILL MAKE THE LENS LOOK LESS
BULBOUS & ALSO REDUCE THE
THE LENS LOOK MUCH.
• THEY ARE EASILY RETAINED IN THE
FRAME AS WELL.
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ASPHERIC LENS DESIGN
• Three dimensional aspheric surfaces are
produced by rotating non- circular curves
about an axis of symmetry.
• The central curvature or vertex curvature of
an aspheric surface is nearly spherical
which is the front curve value utilized for
lens power and surfacing calculations.
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• Away from the vertex curvature, the amount
of surface astigmatism smoothly increases.
• The rate of increase in surface astigmatism
depends upon the degree or type of
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• DEMONSTRATION OF THE SURFACE
CREATED BY ROTATING AN ELLIPSE
ABOUT AN AXIS OF SYMMETRY.
• NOTICE THE CHANGING RADII OF
CURVATURE IN BOTH THE
TANGENTIAL & SAGGITAL PLANES
OF LENS.THIS SURFACE
ASTIGMATISM IS DESIGNED TO
NEUTRALIZE THE OBLIQUE
ASTIGMATISM PRODUCED AS THE
WEARER LOOKS AWAY FROM THE9 May 2014 25
• Proper base curve selection as
recommended by the manufacturer is
critical for an aspheric surface.
• Even the smaller increments of surface
power affect the base curve selection quite
• Consequently, aspheric lenses have more
base curves options.
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Aspheric design for plus and minus
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MEASURING AN ASPHERIC
• Since the curvature of an aspheric surface
varies from the centre to the periphery,
normal measuring instruments cannot
measure the front curve value or vertex
curvature of an aspheric lens accurately.
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• SO WE MEASURE THE LENS POWER
OF AN ASPHERIC LENS IN CENTER
SAGITAL AREA BY THE USE OF
SPHEROMETER & SAG GAUGE.
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PRISM IN ASPHERIC LENS
• The geometric centre of the aspheric lens is
to be aligned with the optical centre of the
• This accurate centering of the aspheric lens,
throws up an issue with the prescribed
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• WHEN PRISM IS GROUND IN AN ASPHERIC
LENS TO DECENTER THE OPTICAL CENTER,THE
OPTICAL CENTER IS MOVED AWAY FROM THIS
REFERENCE POINT-WHICH IS TYPICALLY
LOCATED AT THE GEOMETRIC CENTER OF THE
• HENCE,GRINDING PRISM TO DECENTER THE
OPTICAL CENTER OR DECENTERING THE
OPTICAL CENTER TO INDUCE PRISM IS NOT
RECOMMENDED. HOWEVER, PRESCRIBED
PRISM CAN BE GROUND.
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ASPHERIC LENS FOR APHAKIC
• Aphakics spectacle correction requires powers of + 8.00D to + 15.00D.
• Such a high power correction produces a number of difficulties like:
• Decreased field of view
• Aberration and swimming of object in the field of view
• “Popeye” appearance of patients
• Sensitivity to exact position of the lenses.
• Lens weight and thickness.
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• This all difficulties are solve in aspheric
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• Various design approaches have been applied to cataract lenses.
• There are two main approaches the “foveal philosophy” and the
• Both use the aspheric curve designing.
• Foveal philosophy parallels the standard lens design philosophy,
trying to give the patient the largest possible dynamic field of
view, which is not possible with the spherical curves.
• Therefore, aspheric curves are used.
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ASPHERICS & HIGH-INDEX
• ASPHERICS MAKES THE LENS
SLIGHTLY THINNER THAN THE
CONVENTIONAL SPHERICAL LENS.
• MAKING AN ASPHERIC LENS WITH A
HIGHER-INDEX MATERIAL WILL MAKE
THE LENS FURTHER MORE THINNER.
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• HIGH-INDEX LENS MATERIAL WILL
GIVE THE PROBLEM OF CHROMATIC
ABERRATIONS & MORE SURFACE
• HOWEVER , THE SURFACE
REFLECTIONS CAN BE REDUCED WITH
THE HELP OF „ANTIREFLECTION
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CHECKING LENS POWER IN
• The lens power in case of aspheric lenses can
be measured on the focimeter so that it is
aligned through the geometric centre or middle
of aspheric side of the lens.
• In this area of the lens, the correct power as per
the prescription can be seen.
• As we move away from the geometric centre
of aspheric surface, the prescription alters-
incline with the way the lens surface changes
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• REFRACTIVE INDEX – 1.60
• CENTRE THICKNESS – 5.1 mm
• WEIGHT – 11 Gram
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ASTIGMATISM IS REDUCED
BY ASPHERIC SURFACE ?
• THE POWER CHANGES ALONG THE RADIAL /
TANGENTIAL DIRECTION IS ABOUT 3 TIMES
AS GREAT AS THE CHANGE IN SAGGITAL /
CIRCUMFERENTIAL DIRECTION.THUS ALL
ASPHERIC SURFACES ARE INHERENTLY
ASTIGMATIC AWAY FROM THE CENTER . THE
INHERENT ASTIGMATISM OF ASPHERIC
SURFACE IS USED TO BALANCE THE OBLIQUE
ASTIGMATISM CAUSED BY GAZING OR
SEEING OBLIQUELY THROUGH THE LENS .
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• WITH MOST ASPHERIC SURFACE USED FOR
OPHTHALMIC LENSES,THE CURVATURE
EXTENDING TANGENTIALLY/RADIALLY IN
ALL DIRECTIONS FROM CENTER CHANGES
PROGRESSIVELY & THE CURVATURE IN THE
OPPOSITE MERIDIAN I.e. SAGGITALLY /
CIRCUMFERENTIALLY ALSO CHANGES
PROGRESSIVELY.BUT THE CHANGE IS MUCH
RAPID IN ITS RADIAL DIRECTION.
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• WHEN THE RAYS OF LIGHT FROM THE
OBJECT IN THE PERIPHERY STRIKE ANY
SPHERICAL LENS OBLIQUELY,IT RESULTS
IN ASTIGMATIC FOCUSING ERROR.
• THE TWO FOCAL LINES ARE PRODUCED
FROM EACH SINGLE OBJECT POINT.THE
DIOPTRIC DIFFERENCE BETWEEN THESE
TWO FOCAL LINES IS KNOWN AS „THE
ASTIGMATIC ERROR OF THE SPHERICAL
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• RAYS OF LIGHT FROM AN OBJECT POINT STRIKE
THE SPHERICAL LENS OBLIQUELY & ARE
FOCUSED INTO TWO SEPARATE FOCAL
LINES,INSTEAD OF A SINGLE POINT FOCUS.
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• RAYS OF LIGHT FROM AN OBJECT POINT
STRIKE AN ASPHERIC LENS OBLIQUELY &
ARE FOCUSED INTO A SINGLE POINT
FOCUS.9 May 2014 52
PURPOSES FOR USING AN
• THER E ARE 4 PRIMARY REASONS FOR
PRODUCING A LENS THAT HAS AN ASPHERIC
1.TO BE ABLE TO OPTICALLY CORRECT LENS
2.TO ALLOW THE LENS TO BE MADE
MAGNIFICATION & MAKING IT MORE
3.TO PRODUCE A THINNER & LIGHTER LENS
4.TO MAKE A LENS WITH PROGRESSIVE
OPTICS.9 May 2014 53
ASPHERICITY FOR OPTICAL
• IN HIGH POWERED LENSES IT IS NECESSARY TO USE AN
ASPHERIC LENS DESIGN,TO REDUCE OR ELIMINATE THE
• IN THE MIDDLE,AN ASPHERIC LENS SURFACE STARTS
OUT AS ANY OTHER SPHERICAL SURFACE
STARTS.THEN,AT A CERTAIN DISTANCE FROM THE
OPTICAL CENTER,THE LENS SURFACE GRADUALLY
CHANGES ITS CURVATURE AT A RATE CALCULATED TO
OFFSET PERIPHERAL ABERRATIONS.
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ASPHERICITY FOR OPTICAL
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ASPHERICITY FOR OPTICAL
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ASPHERICITY FOR THINNING
• ASPHERIC „PLUS‟ LENSES ARE
MUCH THINNER AT CENTER
• FOR THINNING A‟PLUS‟LENS
EITHER OR BOTH THE LENS
FRONT OR BACK SURFACES ARE
FLATTENED QUITE A BIT
TOWARDS THE EDGE.
• FLATTENING THE PERIPHERY
MAKES IT POSSIBLE TO GRIND
THE WHOLE LENS THINNER.
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ASPHERICITY FOR THINNING
• ASPHERIC „MINUS‟ LENSES ARE
MUCH THINNER AT PERIPHERY
• FOR THINNING A „MINUS‟ LENS,
THE LENSES FRONT SURFACE IS
STEEPENED OR THE BACK
SURFACE IS FLATTENED
TOWARDS THE PERIPHERY OR
BOTH,WHICH REDUCES THE EDGE
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• BY DEFINATION,ANY LENS SURFACE
THAT IS NOT SPHERIC IS „ASPHERIC‟.
PROGRESSIVE ADDITION LENSES
ACHIEVE THEIR ADD POWER GAIN BY
SURFACE CURVATURE .SO, PAL‟S ARE
ALSO CONSIDERED AS ASPHERIC
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• PAL DESIGNS CONTINUE TO THE
SAME RULES AS DO SPHERIC BASE
CURVE DESIGNS I.e. , THEIR
DISTANCE PORTION WILL HAVE
THE SAME BASE AS THE ONE
WOULD EXPECT FOR SPHERICALLY
BASED CORRECTED LENSES.
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• PALS CAN ALSO BE MADE WITH A FLATTER
BASE ON THE DISTANCE PORTION.TO
AVOID UNWANTED ABERRATIONS,THE
FRONT SURFACE SHOULD BE
ASPHERICALLY COMPENSATED FOR THE
OTHER NONPROGRESSIVE ASPHERIC
LENS,WHICH WILL GIVE RISE TO A MORE
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Asphericity for flattering purpose
• High plus lenses steeper base curve worse lenses look
• Choosing flatter base curve make the lens less bulbous
& decrease magnification.
• Cosmetically look much better.
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• Flattened lens surface is spheric
• Its possible to get both god cosmetic & good
• Eye look like normal or natural
• Decrease magnification or minification
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Good fitting in frame
• Flatter base curve it‟s
easy to keep lens tight in
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• (1) ZOOM LENS
• (2) ASTRONOMICAL TELESCOPE
• (3) DVD PICK-UP
• (4) HIGH POWER LASER
• (5) COLLIMATORS
• (6) LED LENS
• (7) GLASSES
• (8) HIGH QUALITY MAGNIFIER
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• Reduction of oblique astigmatism.
• Magnification of the eye and surrounding structure as
seen by the observer is reduced.
• Spectacle magnification for the patient is also reduced.
• It is flatter , thinner and lighter lens.
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• The lens looks flatter which makes the eyes look
more natural due to reduced magnification or
• Also flatter lens fits better ensuring the attractive
look of the spectacles, thereby, offering the subjects
a wider variety of frames to choose from.
• If the aspheric lens design is coupled with high
index material, it will definitely provide thinner,
lighter and flatter lens that looks cosmetically the
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• Prisms cannot be given in aspheric lenses
• Fitting is quite difficult.
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AVAILABLITY OF ASPHERICS IN
• SEIKO – BI-ASPHERICS
• KODAK ASPHERICS
• GKB ASPHERICS
• SHAMEIR ASPHERICS
• SOLA ASPHERICS
• HOYA ASPHERICS
• ZEISS ASPHERICS
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FITTING GUIDELINES FOR
• USE MONOCULAR PD.
• MEASURE MAJOR REFERENCE POINT
HEIGHTS IN THE CONVENTIONAL
MANNER.THEN SUBTRACT 1mm FOR
EACH 2mm OF PANTASCOPIC TILT.
• MOVING THE OPTICAL CENTER,FOR
PRISMATIC EFFECT,AWAY FROM THE
CENTER OF THE ASPHERIC ZONE
WILL DESTROY ANY ASPHERIC
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Indian companies supplying aspheric
• Roslane meditech – Haryana
• Lensel optic pvt.ltd – Maharashtra
• Optivention international – New Delhi
• Akriti oculoplasty logistics – Andhra
Pradesh9 May 2014 74
• Pupillary distance: Precise monocular PD measurements
position is essential to point the pole of the lens in front of pupil.
• Vertical height: The vertical height of each pupil centre is
marked on the dummy lens of the selected frame.
• Rotation: Rotation of the eye must be considered. This requires
lowering the optical centre based on the pantoscopic angle of the
• The rule is to lower the optical centre 1 mm for every 2 degrees
of pantoscopic tilt.
• However, the maximum drop is 5 mm
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Flatter than the best form spherical surface
• Elimination of large amounts of oblique astigmatism
• Decreased spectacle magnification/ minification as shape factor is
• Increased field of view
• Reduced lens thickness
• Reduced edge substance in negative lenses
• More lightweight
• Good off-axis optical performance
• Controlled distortion
• Better cosmetic
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• ASPHERIC LENSES ARE A HOGHLY
USEFUL GROUP OF LENSES WHICH
PROVIDE VISUAL & COSMETIC
BENEFITS FOR PATIENT.
• ASPHERIC LENSES CAN BE ORDERED
IN HIGH INDEX MATERIAL FOR THE
ULTIMATE IN ATTRACTIVE THIN
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