Aspheric lenses

this presentation give full information of aspheric lenses

1. ASPHERIC LENSES
MADE BY : SWATI PANARA
FROM : BHARTIMAIYA
COLLEGE OF OPTOMETRY
2
nd
YEAR 3
rd
SEMESTER
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2. TERMINOLOGY
•A –NOT
•SPHERIC -SPHERICAL
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3. HISTORY
•In 1909 –Zeiss–Katrallenses.
•In 1958–David Volk –Volk conoidlenses.
•In 1970s –Robert Welsh –Welsh 4 drop
lenses.
•1976 –Davis and Fernald –patented a
series of aspheric lenses .
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4. •In 1980 –Whitney , Reilly and Young
patented Fulvue aspheric blended
Lenticular lenses .
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5. INTRODUCTION
•The literal meaning of “aspheric” is simply
“not spherical”, which means cylinder
surfaces or toroidal surfaces used for
astigmatic correction.
•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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8. •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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9. •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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10. PRINCIPLE
•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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11. Conic section
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12. Conic section
•Four types of conic section:
1.Circle
2.Ellipse
3.Parabola
4.hyperbola
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13. CIRCLE CONIC
SECTION
It‟sformedbyhorizontalplane
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14. Ellipse conic section
It‟s formed by angle plane through cone
don‟t intersect the base of cone.
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15. Parabola conic section
Intersectionofconewithplanehaving
onesideparalleltothesideofcone.
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16. Hyperbola conic section
Intersectionbyplanethatmakesofcone
thanthesideofconemakewithitsbase.
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17. WHY ASPHERIC
•Unfortunately several lens aberrations affect
the quality of peripheral vision through a
spectacle lens.
•Oblique astigmatism is the principal lens
aberration that is considered to be the most
serious defectin designing theophthalmic
lens.
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19. •When the rays of light strike the periphery
of the lens obliquely, two focal lines are
produced from eachsingle object point.
•The dioptric difference between these two
focal lines is known as the astigmatic error
of the lens.
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21. •CHOOSING A FLATTER BASE CURVE
WILL MAKE THE LENS LOOK LESS
BULBOUS & ALSO REDUCE THE
MAGNIFICATION.COSMETICALLY,
THE LENS LOOK MUCH.
•THEY ARE EASILY RETAINED IN THE
FRAME AS WELL.
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22. 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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23. •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
asphericity.
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25. •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 THE
LENS
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26. TANGENITAL & SAGITAL
PLANE
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27. •Since, flattening a lens introduces
astigmatic and power error, the peripheral
curvature of the aspheric surface should
change in a manner that neutralizes this
effect.
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28. •AT A GIVEN DIAMETER,AN ASPHERIC
SURFACE HAS A SHALLOWER SAG
THAN THE SPHERICAL SURFACE.
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30. •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
considerably.
•Consequently, aspheric lenses have more
base curves options.
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32. Aspheric design for plus and minus
lenses
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33. MEASURING AN ASPHERIC
SURFACE
•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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35. •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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36. CONVENTIONAL INSTRUMENTS
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SAG GAUGE

37. PRISM IN ASPHERIC LENS
•The geometric centre of the aspheric lens is
to be aligned with the optical centre of the
patient‟s eyes.
•This accurate centering of the aspheric lens,
throws up an issue with the prescribed
prism.
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38. •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
LENS.
•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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39. ASPHERIC LENS FOR APHAKIC
PATIENT
•Aphakics spectacle correction requires powers of + 8.00D to + 15.00D.
•Sucha high power correction produces a number of difficulties like:
• Magnification
• 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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40. •This all difficulties are solve in aspheric
lens design.
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41. •Various design approaches have been applied to cataract lenses.
•There are two main approaches the “foveal philosophy” and the
“peripheral philosophy”.
•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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42. POSTCATARACT ASPHERIC
LENS
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43. 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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44. •HIGH-INDEX LENS MATERIAL WILL
GIVE THE PROBLEM OF CHROMATIC
ABERRATIONS & MORE SURFACE
REFLECTIONS.
•HOWEVER , THE SURFACE
REFLECTIONS CAN BE REDUCED WITH
THE HELP OF „ANTIREFLECTION
COATING‟.
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45. CHECKING LENS POWER IN
ASPHERIC LENS
•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
power.
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46. PROPERTIES
•REFRACTIVE INDEX –1.60
•CENTRE THICKNESS –5.1 mm
•WEIGHT –11 Gram
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47. HOW OBLIQUE
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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49. •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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50. OFF-AXIS PERFORMANCE
•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
LENS‟.
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51. OFF-AXIS PERFORMANCE
•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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52. OFF-AXIS PERFORMANCE
•RAYS OF LIGHT FROM AN OBJECT POINT
STRIKE AN ASPHERIC LENS OBLIQUELY &
ARE FOCUSED INTO A SINGLE POINT
FOCUS.
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53. PURPOSES FOR USING AN
ASPHERIC DESIGN
•THER E ARE 4 PRIMARY REASONS FOR
PRODUCING A LENS THAT HAS AN ASPHERIC
SURFACE.
1.TO BE ABLE TO OPTICALLY CORRECT LENS
ABERRATIONS
2.TO ALLOW THE LENS TO BE MADE
FLATTER,THEREBY REDUCING
MAGNIFICATION & MAKING IT MORE
ATTRACTIVE.
3.TO PRODUCE A THINNER & LIGHTER LENS
4.TO MAKE A LENS WITH PROGRESSIVE
OPTICS. 9 May 2014 53

54. ASPHERICITY FOR OPTICAL
PURPOSE
•IN HIGH POWERED LENSES IT IS NECESSARY TO USE AN
ASPHERIC LENS DESIGN,TO REDUCE OR ELIMINATE THE
PERIPHERAL ABERRATIONS.
•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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55. ASPHERICITY FOR OPTICAL
PURPOSE
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PERIPHERAL
ABERRATIONS
SEEN IN
NORMAL
SPHERICAL
LENS

56. ASPHERICITY FOR OPTICAL
PURPOSE
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PERIPHERAL
ABERRATIONS
ABSENT IN
ASPHERIC LENS

57. ASPHERICITY FOR THINNING
PURPOSE
•ASPHERIC „PLUS‟ LENSES ARE
MUCH THINNER AT CENTER
THAN CONVENTIONAL
SPHERICAL LENS.
•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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58. ASPHERICITY FOR THINNING
PURPOSE
•ASPHERIC „MINUS‟ LENSES ARE
MUCH THINNER AT PERIPHERY
THAN CONVENTIONAL
SPHERICAL LENSES.
•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
THICKNESS CONSIDERABLY.
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59. ASPHERICITY FOR
PRODUCING PROGRESSIVE
POWER CHANGES
•BY DEFINATION,ANY LENS SURFACE
THAT IS NOT SPHERIC IS „ASPHERIC‟.
PROGRESSIVE ADDITION LENSES
ACHIEVE THEIR ADD POWER GAIN BY
PROGRESSIVELY STEEPENING
SURFACE CURVATURE .SO, PAL‟S ARE
ALSO CONSIDERED AS ASPHERIC
LENSES.
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60. •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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61. •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
COMPLEX DESIGN.
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62. Asphericity for flattering purpose
•High plus lensessteeper base curve worse lenses look
•Choosing flatter base curve make the lens less bulbous
& decrease magnification.
•Cosmetically look much better.
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63. •Flattened lens surface is spheric
•Its possible to get both god cosmetic & good
optics
•Eye look like normal or natural
•Decrease magnification or minification
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65. Good fitting in frame
•Flatter base curve it‟s
easy to keep lens tight in
frame.
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66. USES
•(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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67. Benefits
•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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68. •The lens looks flatter which makes the eyes look
more natural due to reduced magnification or
minification.
•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
best.
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69. Disadvantages
•Prisms cannot be given in aspheric lenses
.
•Expensive.
•Fitting is quite difficult.
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70. AVAILABLITY OF ASPHERICS IN
INDIA
•SEIKO –BI-ASPHERICS
•KODAK ASPHERICS
•ESSILOR(NIKON)ASPHERICS
•GKB ASPHERICS
•SHAMEIR ASPHERICS
•SOLA ASPHERICS
•HOYA ASPHERICS
•ZEISS ASPHERICS
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71. •RODENSTOCK ASPHERICS
•YOUNGER OPTICS(TRIVEX)
•TRANSITIONS
•DELTA ASPHERICS
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72. FITTING GUIDELINES FOR
ASPHERICS
•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
OPTICAL ADVANTAGE.
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74. Indian companies supplying aspheric
lenses
•Roslane meditech –Haryana
•Lensel optic pvt.ltd –Maharashtra
•Optivention international –New Delhi
•Akriti oculoplasty logistics –Andhra
Pradesh
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75. DISPENSING TIPS
•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
frame.
•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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76. SUMMARY
Flatter than the best form spherical surface
• Elimination of large amounts of oblique astigmatism
• Decreased spectacle magnification/ minification as shape factor is
reduced
• 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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77. CONCLUSION
•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
LENS.
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