clinical optics

1. Ophthalmiclensmaterialandtheirclinical
significances
MODERATOR PRESENTERS
NIRAJDEVJOSHI MANOJMAHAT
SABINAKHATUN

2. Presentation layout
 Introduction
 Types of ophthalmic lens material
 Glass and its varities

3. Introduction
 Ophthalmic lens is the portion of the transparent medium bounded by two
refracting surfaces at least one of which is curved

4. Properties of ophthalmic lenses
 Optical properties
 Mechanical properties
 Electrical properties
 Chemical properties
 Thermal properties

5. Optical properties
 Defines how the material interacts with light.
Includes
 Abbes number
 Refractive index
 Reflectance
 Absorption

6. 1.Abbes number
 Measure of the degree to which light is dispersed when entering a lens
material
 It is the property of lens material and not affected by any surface technique
 Abbes number is reciprocal of dispersion
 Also called as constringence / V number
 Dispersion (w) = nF – nC /nD -1
 Higher the abbes number lower is the chromatic aberration in the lens
 Abbes number>5ois crown glass & < 5o is flint glass

7. 2.Refractive index
 Ratio of velocity of light in air to the velocity of light in a medium
 Describe the ability of lend to bend light
 Higher the refractive index of material more it will bend the light
That’s why high index lenses decreases the thickness of the lenses

9. 3.Reflection
 Light reflectance occur at each of the lens surfaces
 Result in the loss of lens transparency and undesirable reflections
on the lens surfaces
 Reflectance = 100 (n -1)2/(n+ 1) 2 %
 For crown glass reflection is 4%
 The higher the refractive index the greater the proportion of light
reflected from the surfaces

10. Refractive index % of light reflected
1.5 7.8 %
1.6 10.4%
1.7 12.3%
1.8 15.7%
1.9 18.3%
 That’s why antireflection coating is must in high index lenses

11. 4.Absorption
 The percentage of light absorbed between the front and the rear lens
surface
 It occur according to Lamberts law and varies exponentially as the
function of lens thickness i.e Iq = I0(q)x

12. Mechanical properties
 Specific gravity
 Impact resistance
 Scratched resistance

13. 1.Specific gravity
 Ratio of 1 cubic cm of a material to 1 cubic cm of water
 Higher the specific gravity of a lens material higher will be the
density and heavier will be the lens
 Give a rough idea about the relative weight of various lens

14. 2.Impact resistance
 Susceptibility of lens material to fracture under stresses applied at high
speed
 Relative impact resistance of various material will vary depending on the
size and shape of the missile in the test
 The standard test employed by FDA is Drop ball test

15. Drop ball test
 5/8 inch steel ball
 Weight approx. 0.56 ounch
 Dropped from a height of 50 inches
 Strike within a 5/8 inch diameter circle located at he geometrical
center of the lens
 To pass this test lens must not fracture
 Polycarbonate > high index plastic lenses > CR -39 > ordinary
glass lenses

17. Tempering
 Any treatment that places the lens under compression provides the
lense with greater impact resistance than that possessed by
ordinary annealed glass
Types
 Thermal tempering
 Chemical tempering

18. Thermal tempering
 Finished lenses is heated to 650 degree and rapidly cooled by blast
of air on both sides
 surface quickly becomes rigid with cooling
 Surface is under compression with resulting tension in internal
surface
 Birefringence under polariscope characterized as maltese cross
patterns

20. Chemical tempering
 Ion exchange method
 Exchange small ions in the glass with larger ions in the molten salt bath
below strain temperature
 Crown glass lenses the Bath consists of 100% kno3 and sodium ions na+ in
the lens is replaced by larger potassium ion present in bath
 Corning photochromatic lens bath consists of 40 % Nano3 and 60% Kno3
 Temperature much less than thermal tempering (400-470degree )
 Lower temperature means less lens warpage and fewer irregularities

22. Differences
Thermal tempering Chemical temparing
1. No resurfacing and re-edging Requires re -edgng and resurfacing
2. Not as much impact resistance 2-3 X more impact resistance
3. Much faster and takes only mins Originally takes 16 hours
4. Maltese pattern visible under Peripheral band visible under polariscope
Polariscope
5. Temperature 650 Temperature(400-450 )

23. 3.Scratch resistance
 Glass lenses are abrasion resistance
 Plastic lenses needed to be coated with an additional resin to
approach the scratch resistance of glasses
 Premium hard coating >Ziess> Crizal > Teflon

24. Electrical properties
 Characterized the effects of electromagnetic waves and electricity on
the material
Chemical properties
 The reaction of the materials to the chemical substances usually
found during lens manufacture
Thermal properties
 Characterised changes of state and effect of temperature on material

25. Lens material
 All the material used during manufacture i.e all materials entered into the
composition of the basic ophthalmic lens
 Types of lens material
 Natural media
 Glass
 plastic

26. Natural media
 It includes quartz or rock made out of pure silica
 Its hardness and low mist retaining property made it ideal for
spectacle lens
 Not used in optical instrument since it is double refracting
medium
 Clear natural crystal are very rare to find
 So their use is almost stopped

27. Glass
 An amorphous solid material that is obtained by cooling without
crystallization , an organic mixture that has been found to fuse at high
temperature
 Also called super cooled liquid
 Raw material
- quartz (sand )
-Soda (sodium carbonate
-Lime(carbon dioxide)
- trace amount of potassium , arsenic ,antimony and borax

28. Manufacture
 Glasses are manufactured by two process
 Batch process
 Continuous process
 Both of these process involve the following steps
molting , fining, stirring ,Anealing ,inspection ,ground &polising

29. Put major ingredient & cullet in melting pot (36 inches diameter 32 inches heigth
1. Batch process
Raise temperature of pot to 800-1000 & keep for 3-5 days
Add ingredients at interval till temperature raised to 1400
At the end of melting and fining ,skim of unwanted materials and stir the remaining melt
with long clay rods

30. Cool to temp 1200 ,pour and roll into sheet of various thickness .place it in heated
annealing oven and gradually cool to room temperature
Cut into small pieces ,reheat and mould into rough blanks
Ground and polish the front surface of shell into desired curvature
Reblocked the blanks , ground and polished on second side
 For production of small quantities of glass e.g high index glass

32. 2. Continuous flow process
 The molten glass is not poured jnto sheets
 Extruded by means of a continuous process and pressed into molds
to make rough blanks
 To produce large quantities of particular type of glass

33. Types of glass
 Crown glass
 Flint glass
 Barium crown glass
 High index glass
 Absorptive glass
 Photochromic glass
 Polarised glass

34. Crown glass
 Contains 70 % silica ,14-16 % sodium oxide .11-13% calcium
oxide and small percentage of potassium ,borax ,antimony ,arsenic
 Used for single vision glass
 Distance portion of bifocal and trifocal
 Most widely used in ophthalmic industry

35. characteristics
 Refractive index = 1.523
 Abbes number =59
 Specific gravity=2.54
 Transparency=91.6%
 U.V abortion=280nm

36. Advantages
 Highly scratched resistance
 Resistance to solvent and temperature fluctuation
 Good optical quality
 High range curves blanks and addition available
 Available in photochromic sunglass option
 Low in cost
 Produce least amount of chromatic aberration
 Blanks available in all sizes

37. Disadvantages
 Low impact resistance
 Heavier material
 Chips can easily form while edging and handling
 Not appropriate for soldier and sport wear
 U.V absorption not 100%

38. Flint glass
 Ingrediants
 45-65% lead oxide
 25-45% silica
 105 soda +potassium oxide

39. Types Refractive index Abbes
number
Specific gravity
Dense flint 1.649 33.8 3.90
Extra dense flint 1.69 30.9 4.23

40. Advantages
 Used in kryptok bifocal
 High prescription
Disadvantages
 High dispersion
 High specific gravity so heavier
 Transparency less than crown glass

41. Barium crown glass
Ingrediants
 25-40% barium oxide
 30% silica
 Trace amount of lime ,zinc , alumunium, boron and zirconium
 Use – in segment of Nokromes series of fused bifocal

42. Types Refractive Abbes value Specific
Light barium 1.573 57.4 3.21
Dense barium 1.616 55.1 3.36

43. Advantages
 High refractive index without an appreciable increase in
chromatic dispersion
Disadvantages
 Chromatic dispersion more than crown glass

44. High index lenses
 The term high index refers to the lenses whose index of refraction is
higher than 1.523 in glass and 1.49 in plastic

45. classification
 Normal index =1.48 to 1.53
 Mid index = 1.54 to 1.63
 High index = 1.64 to 1.73
 Very high index =1.74 to above

46. Glass high index
 Contents high% of titanium oxide
 Transmission less than 92%
 Useful for reducing the thickness for high powered lenses
Plastic high index
 Some plastic high index are made from polyurethane
 Made up of thermosetting plastics
 Most cosmetically acceptable lenses

47. Optical properties of high index glasses
compared to crown glass
Suppliers Glass R.I Abbes no. Specific gravity
Numerous crown 1.52 58.9 2.54
Hoya Lh 2 1.6 42.5 2.58
corning Photogray
extra 16
1.6 42.2 2.73
Rodenstock High crown 1.604 41.8 2.67
pilkington Slimeline
750
1.704 51.0 3.38
schott High -lite 1.706 31.0 2.99

48. High index lens design
 It is most commonly available in multiple progressive and single
designs
 Aspheric and atoric design are also becoming readily available to
the eye care provider in high index material
 High index is also available with polarization or photochromatic
options

49. When to recommended high index lenses
 High index lens materials for any patient with a prescription of +/-
3.00 diopters or more
 People who are self conscious about the thickness of their lenses
 People who wear contacts because of traditional lenses distort their
eyes

50. Advantage of high index lenses
 Power rings round the edges of the lenses is reduced
 Reduce thickness
 Look flatter
 Thinner
 Lighter
 The benefit is greater peripheral vision as well as less
magnification/minification of the eye

51. Disadvantages
 Low abbes number so increase chromatic aberration
 Poor light transmission and increased backside and inner surface
reflection increasing so importance of anti reflective coating
 More expensive than normal glass
 Greater distortion away from the optical centre

52. Absorptive glass
 Made by addition of metallic oxides to the raw materials in the
batch .
 Addition of different metal provide different color
cobalt – blue
chromium oxide –green
magnesium oxide –violet
uranium oxide – yellow
cerium oxide – UV absorption
iron oxide – IR radiation

53. properties
 Reduces the amount of transmitted light or radiant
energy
 Acts as a filter
 May be uniform or neutral, absorbing light of all
wavelengths equally
 May be selective, absorbing light of certain
wavelengths more than others

54. Major forms of absorptive lenses
1. Tinted solid glass lenses
2. Glass lenses with surface coatings
3. Tinted plastic lenses
4. Photochromatic lenses
5. Polarizing lenses

55. Photochromatic lenses( glass)
 Contain silver halide crystal
 On exposure to uv light silver halide separates into silver and
halogen ions
 The dissociated silver halide regroup to form opaque silver colloid
 The opaque silver halide colloid absorb visible light and
photochromatic lenses becomes dark
 In absence of uv light the silver and halide crystals recombine and
the lenses fades

56. Advantages
 Helps eye to cope up as they react to different light conditions during
day time.
 Are immune to fatigue or deterioration of their photochromic
performance with extended use.
 Are available in single vision, bifocal & varifocal forms
 Gives visual comfort indoor & outdoor

57. DISADVANTAGES
 Do not adjust immediately
 Losses its darkening ability with time
 Cant replace sunglasses because temperature increases reaction
slows
 Do not darken under vehical because windscreen absorb uv light

58. POLARIZING LENSES
 Polarized lenses are transparent pieces of material usually glass or
plastic that blocks certain types of light waves
 Light reflected from surfaces like a flat road is generally
horizontally polarized
 This horizontally polarized light is blocked by the vertically
polarizer in the lenses . The result is the reduction in the annoying
and sometime dangerous glare.
 Occurs at the Brewsters angle i.e tan i=n

59. Recommendation of polaroid lenses
 Day time driver
 Fisherman
 At beach /sea shores
 Snowfield worker
 Good for UV protection

60. Limitations
 Do not provide universal protection from glare
 Because the polarizing stripes reduce the amount of light entering
the eye , these lenses should not be used at night
 can cause headache and eyestrain
 Do not usually work with snow glare because snow tends to reflect
light equally in all directions

62. PRESENTATION LAYOUT
1. Introduction
2. History
3. Types on the basis of physical properties
4. Plastic materials
5. Summary
6. References

63. Plastics
 Polymeric material of large molecular
weight which can be shaped by flow.
 Also called as organic material
 Synthetic materials formed by combining various organic ingredients with inorganic material such
as carbon ,hydrogen , oxygen, nitrogen, Sulphur , etc

64. History
 Just as World war 1 served as the impetus for the development of Optical
glass industry, World war 2 served as the impetus for the development of the
plastic industry.
 Plastic material developed during the World war 2 were PMMA and later
develop CR-39 for use in military aircraft.
 In 1947 Robert Graham, formed the Armor-lite Lens Company in Pasadena
and California & later described the first ophthalmic lenses made from CR-
39(scratches more easily than glass, is much more scratch resistant than
PMMA)

65.  In 1957 General Electric developed a new plastic material, a polycarbonate
resin, called Lexan, which has great mechanical strength and high service
temperatures.
 In 1982 corning glass works announced the development of a lens called
Corlon , a two layered ophthalmic composite material consisting of a
glass lens backed by a thin layer of polyurethane film

66. Types
 Two types of plastic on the basis of physical properties.
 Thermoplastic material
 Thermosetting material

67. Thermoplasticmaterial
-soften when heated and can be remolded.
-have their molecule arranged in long chains and usually supplied in pellet, granular or sheet form.
-the material can be stretched ,pressed ,molded into complex shapes with no appreciable change in
chemical structure.

68.  Since no chemical changes occur so softening and hardening cycle may be
repeated indefinitely
 Less dimensionally stable ,withstand less heat without deformation.
 Examples include acrylates (plexiglass, Lucite and PMMA), cellulose acetate ,
cellulose nitrate ,polycarbonate ,nylon , polystyrene and vinyls .

69. Thermosettingplasticmaterial
 Once heated and molded, these plastics cannot be reheated and remolded.
 The molecules of these plastics are cross linked lattice pattern
in three dimensions and this is why they cannot be reshaped
 The bond between the molecules is very strong.
 Difficult to recycle.

70.  Once hardened the material can’t be softened*.
 If subjected to high temperature ,material decomposes without melting.
 Good dimensional stability , rigid , relatively insensitive to heat ,relatively hard surface.
 Example include Columbia Resin-39, Bakelite , melamine(used for tableware.)

71. Commonlyusedplasticmaterial
1. Polymethyl methacrylate (PMMA)
2. Corlon
3. Polycarbonate
4. CR-39
5. Trivex
6. High index plastics

72. 1. PMMA
 PMMA - Poly Methyl Methacrylate (C₅O₂H₈)n
 It is a thermoplastic and transparent plastic.
 has a refractive index of 1.490
 Chemically, it is a synthetic polymer of Methyl Methacrylate
 Preparation: Suspension polymerization and Radical polymerization

73. Clinicaladvantages
 High degree of transparency
 Half the weight of glass
Disadvantages
 Became soft and deformed in hot climates
 More liable to abrasions

74. TransparentProperty:
 Density of PMMA: 1150 - 1190 kg/m³
 Density of Glass: 2400 - 2800 kg/m³
 It can transmit 97% of visible light ( 3-mm thickness)

75. Contd..
 Daylight Redirection: PMMA can be used in laser - cut panels to redirect sunlight
into a light pipe and then spread it into a room.

76. 2.Corlon
 Special type of lens made from plastic and glass lens
 Front is glass* and back is plastic*
 Lenses are manufactured as C-Lite lenses
 Advantages
 25% thinner than conventional lenses
 25% lighter than all glass lenses
 * glass-crown
 *Plastic- polyurethane

77. 3.Polycarbonate
 The first alternate plastic material was polycarbonate
 It is a high index plastic lens
 Gives extra level of protection to the lens wearers
 Usually preferred for children and sportswear

78. Manufacturing process
 Polycarbonate is a thermoplastic material so it begins as solid and is melted down and is then injected into
a mold at a temperature of 3200 C
 In the injection process, the polycarbonate conforms, under pressure, to the highly polished metal surfaces
of the injection mold
 A device will squeeze the lens to prevent lens shrinkage and ensure optical accuracy
 After removal from the molds, the lenses are inspected and processed through a coating machine

79.  Because the surface hardness of polycarbonate is much softer than CR-39, all
polycarbonate lenses receive hard coating
 After the coating process is completed, a heat curing process produces
polymerization and cross linking of the coating
 The coating solvents evaporate, leaving behind a silica based solid coating
approximately 4-6 µm thick

81. ClinicalAdvantages
1.High Refractive index i.e 1.586
 So lens are thinner
2.Low specific gravity i.e 1.20
 So lighter and thinner lens in high prescription
3.Polycarbonate lenses absorb ultraviolet radiation upto 380nm without additional treatment
4.High impact resistance so tremendiously beneficial where safety is the primary concern I.e for children,
monocular individuals, industries and sportsperson

82. Disadvantages
 Due to high index increase lens reflections
 Difficulty in molding to free from waves and blemishes
 Difficulty in edging and beveling

83.  Polycarbonates are soft and scratches very easily
 Having a higher index of refraction may produce more reflections than ophthalmic
crown glass or CR-39
 Low Abbe number(30) so produces undesirable lateral chromatic aberration upon
peripheral gaze.

84. ImpactResistanceofPolycarbonate
 Polycarbonate is impact resistance because its molecules are extremely long chains
of atoms that can slide back and forth on each other, with the result that the
material can be flexed and even deformed without breaking
 Stephens and Davis showed that polycarbonate has 21 times the impact resistance
of CR-39 for ¼ inch and 1/8 inch steel balls fired at high speed

85. 4.CR-39
 CR stands for Columbia Resin developed by the Columbia resin project of (PPG) industries back in
1940.
 Number 39 denotes the type of Columbia Resin used.
• For years CR- 39 was used without anti-scratch coating
• It was developed by (PPG) Pittsburgh Plate Glass industries.
 Good optical quality, with a high V-value and is easy to surface, edge, drill and coat.
.

86. • It is the thermosetting material
• Now, however, most CR-39 lenses come with an anti scratch coating, making the
material much more scratch resistant.
• CR-39 plastic lenses do not fog up as easily as glass lenses.
 For smaller, high velocity, sharply pointed objects, CR-39 lenses perform better
than chemically tempered glass

87. Manufacture
 Ophthalmic lenses made of CR-39 are cast from allyl di-glycol carbonate monomer
 Supplied as yellow viscous liquid
 Some add a copolymer or other additives, such as anti yellowing agents, ultraviolet absorbers
and mold releasers
 These copolymers may reduce lens shrinkage, make casting easier and make lens tougher and
lighter

 After catalyst and other ingredients are added, the liquid resin is poured into a glass mould having
a concave and a convex surface

88.  The inside surface of the mold are highly polished to produce finished lens surfaces of high
quality
 The entire mold is then placed in an oven and subjected to a controlled time/temperature
relationship : the cure cycle
 After completion of the cure cycle, the molds are removed from the oven, dismantled and
separated from the finished lens
 Lower temperatures and longer curing times result in lenses having superior rigidity,
dimensional stability, impact resistance and scratch resistance

89. Liquid monomer is mixed with a catalyst,
placed in molds & heated

90. OpticalpropertiesofCR39
 Refractive index = 1.498
 Abbe value = 58
 Specific gravity = 1.320
Clinicaladvantages
1.Lightness
 Low specific gravity
2.Impact resistance
 Pass FDA impact resistance test

91. Contd..
3.Chemical inertness
 Resistance to all chemical solvents except highly oxidizing agents
4.Resistance to fogging
 Due to low thermal conductivity
5.Tintability
 Tint or re-tint or remove

92. 6. Versatility in optical design: examples include aspheric surfaces for cataract lenses,
magnifiers with aspheric surfaces, progressive addition multifocal lenses etc.
7.Resistance to pitting
 Welding spatter or particles

93. Disadvantages
1.Surface abrasion
 Low resistance to surface abrasion
2. Warpage upon glazing
3. Increased thickness

94. 4. Inferior photochromic properties
5. Index variability with temperature
 Change in RI as a function of temperature is 50 times greater than of optical glass
making CR-39 less stable in thermally fluctuating environments

95. ImpactResistanceofCR-39
 With ballistics tests using a 1/8 inch steel ball, it was found that a 3mm CR-39
lenses were more impact resistant than air tempered glasses
 Welsh et al tested untreated glass, air tempered glass, chemically tempered glass
and CR-39 plastic lenses with a ballistic device using a 3/8 inch missile and found
the CR-39 to be the most impact resistant and untreated glass to be the least

96. 5.TRIVEX
 Trivex lenses developed by PPG industries, Inc
 The lens material was originally for military use.
 The lens material to provide excellent safety for window in combat vehicles and good optics.
 Similar to polycarbonate but have higher quality optics & thus provide clearer vision.
 Commercial brands-
 Hoya as the Phoenix material,
 Younger Optics as Trilogy®,
 Augen Optical as Trinity™,
 Thai Optical as Excelite TVX™,

97. Opticalproperties
• Refractive index – 1.523
• Abbe value – 35 to 43
• Density – 1.11
 Trivex is a very new lens material that exhibits three very good lens characteristics,
therefore its name Trivex.
 Trivex is also known as Trilogy and phoenix.
I. First, it is the lightest weight of all plastic materials.
II. Second, it has impact resistance at least equal to polycarbonate.
III. Third, it has an excellent abbe value.

98.  Excellent Optics
incorporates UV protection.
Edges can be polished.
the material can be coated for scratch protection and anti-reflection
and tinted
Available in single vision, aspheric, bifocal, and a limited number of
progressive lens designs.
 It is the lens of choice for drill- mounted lenses because it does not
crack or split at the drilled hole.

99. Minimaldisadvantages.
inability to be tinted darker
because it has a 1.53 index, lenses may have very
slightly thicker edges than other materials,

100. 6.HIGHINDEXPLASTICLENSES
High Index lenses
Lenses of plastic or glass material having higher index of
refraction.
Characteristics
Light weight
Thinner
Comfortable
Attractive

101. Contd…
• High index Plastics are made up of Thermosetting plastics.
• These lenses have higher than standard refractive index.
• Most cosmetically acceptable lenses.
 High index lenses are available in glass or plastics.

102. • It enable the lens to bend light “faster” than other.
 The higher the index of lens material, the thinner and light-
weight the lens is.
 The thinnest, light weight lenses are typically the most
expensive.

103. Opticalcharacteristics
 Refractive index – 1.640-1.740
• Abbe value – 42-32
• Density – 1.3-1.5
 UV cutoff- 380nm-400nm
 Advantages
• Cosmetically good
• Magnification is reduced
• Thinner and lighter than other lenses
 Available in range of lens type including photochromatic ,
multifocal etc
• Impact resistant

104. Disadvantages
• Greater distortion
• Not available in larger blank size
• More chromatic dispersion
• Off axis aberration are seen
• Expensive

105.  From crown glass (n=1.523) to high index lenses (n=1.90), the annoying
reflection rises 8% to 20%.
Twice as much as crown glass.
 An AR coating is a must for lenses with high index materials.
 Refractive index and reflectance per lens surface

106. Nikon Plastic High Index lenses
 Nikon Lite DXII
The world's lightest lens. This is a mid-index lens that is 40% lighter and
28% slimmer than conventional plastic.
 Nikon Lite IV
Lightweight, super-thin high index lens. 29% lighter and 40% thinner than
conventional plastic.
 Nikon Lite V
50% thinner than conventional plastic.
 Nikon Pointal
Ultra slim glass is 45% thinner for the best cosmetic appearance

107. Plasticphotochromiclens
 1st commercially successful photochromic lens produced by Transition optical in
1991,the plastic versions are getting increasingly commercialized.
 Rather of silver halide crystals , it uses organic dyes (indolino spirorazines i.e.
INS)
 When activated by UV rays, the INS molecules scatters absorbing sunlight &
reducing amount of visible light .
 When removed chemical reaction reverse & lens return to its clear state.

108. Materials used in Contact lens
 Hard lens material
Manufacture from plastic or thermoplastic material.
The first commercially available contact lens material was
PMMA (poly methylene meth acrylate).
 Rigid gas permeable lens material –
 Earlier
 Cellulose acetate butyrate –thermoplastic
 Silicone
 Styrene

109. Presently RGP material
A. Silicone acrylate
Commonly manufactured from copolymer of PMMA and
silicone containing vinyl monomer
B. Fluoropolymers
Made from copolymer containing fluorine
High oxygen permeability
Not prone to surface deposits

110. Hydrophilic soft lens material
 Soft lens are made of hydrogels containing hydroxyl groups
A.HEMA lenses
 Original soft lens material
 Resistant to biodegradation and withstand chemical and thermal
sterilization
B.HEMA VP lenses
 Mixture of HEMA and Vinyl pyrro-lidone (VP)
 Tendency to color with age

111.  C. MMA-PVD lenses
 Made of hydrophilic polymer PVP ,monomer VP and hydrophobic MMA
 D. Glycidyl Methacrylate
 Combination of HEMA and VP or with MMA and VP

112. Intraocular lenses material
1.Rigid PMMA IOLs
• Commonly used material for manufacture of IOL is PMMA.
• Rigid ,non -foldable and hydrophobic(water content<1%)
• Chemically stable compound
• Specific gravity is much low( ie 1.2), much lower than heavier
glasses
• Disadvantages include variation in temperature and water
absorption
• Because of the required large incision, PMMA IOLs are seldom
preferred today.

113. 2. Foldable IOLs
 Became popular after the success of phaco-emulsification
 Available in different designs and are made up of:
A . Silicone IOLs:
 Made up of Polyorganosiloxane
 Low Index of refraction- 1.43
 Silicone lenses have been suspected to favor bacterial adhesion, with
increased risk for postoperative infection, so not in use in modern days

114. B. Hydrophobic Foldable Acrylic
 Hydrophobic foldable acrylic materials are a series of copolymers of
acrylate and methacrylate derived from rigid PMMA, with the purpose of
making them foldable and durable.
 refractive index between 1.44 and 1.55.
C.Hydrophilic Foldable Acrylic
 Hydrophilic acrylic materials are composed of a mixture of
hydroxyethylmethacrylate (PHEMA) and hydrophilic acrylic monomer
 Hydrophilic acrylic lenses are soft, somewhat compressible, and have
excellent biocompatibility because of their hydrophilic surface.
 Hydrophilic acrylic IOLs are the most popular worldwide, especially in the
US because of the FDA approval.

115. Comparisonsbetweenglass&plastic
S.N
Glass lens Plasticlens
1 Heavy Light weight
2 Low impact resistance High impact resistance
3 Lower Scratchresistant Highly scratchresistant
4 Cheaper Costlier
5 3 piece cantbe used 3piece can be used
6 Aberration is low Aberration is high
7 Higher tendencyto fog Lower tendency
8 Less transmission 2% greater transmission
9 Coating isn’t a necessity Coating is must
10 Not preferredfor children Preferredfor children

116. PlasticsorGlass
 So due to inherent lightness and safety, plastics has almost completely replaced glass as the first
choice of spectacle lens material
 Today in most of the developed world, some 95% of spectacle lenses are made from plastics
materials
 However glass is still in use with very high indices in excess of 1.80, and to photochromic lenses
with specialized properties, such as Corning’s CPF glasses.

117. References
 Clinical Optics- Troy E. Fannin , Theodore Grosvenor
 System of ophthalmic dispensing- Clifford W. Brooks , Irvin M. Borish
 Essentials of ophthalmic lens finishing- Clifford W. Brooks
 CET articles
 Internet

119.  Happy Holi