Diabetic ophthalmopathy

1. Qazi Muhammad Omair
Lecturer OD
1

2.  It is the portion of the transparent medium
bounded by 2 refracting surfaces at least 1 of
which is curved.
2

3.  Ophthalmic lens materials means all materials used
during manufacturing, i.e. all materials entered into
the composition of the basic ophthalmic lens.
 There are three types of lens material.
 (1) NATURAL MEDIA
 (2) GLASS
 (3)PLASTIC
3

4. NATURAL
MEDIA
GLASS
PLASTIC
4

5.  Quartz or rock made out of pure silica was
exclusively used
 Its hardness and low mist retaining property made
it ideal for spectacle lens
 Not used in optical instruments since it is doubly
refracting material
5

6. 6

7. 7

8. 8

9.  Clear natural crystals
of quartz are very
rare to find
 So their use is almost
stopped
9

10. Glass lenses Plastic lenses
 Heavy
 Low impact resistant
 Scratch resistant
 Cheaper
 3 piece can’t be use
 Not proffered for children
 Light weight
 High impact resistant
 Highly Scratch resistant
 Costlier
 3 piece can be use
 good proffered for children
10

11. Glass lenses Plastic lenses
 Less transmission
 Aberration is low
 Higher tendency to fog

 More affected
 It not necessary required
coating
 2% greater transmission
 Aberration is high
 Lower tendency to fog
 Less affected
 must necessary required
coating
11

12.  Amorphous compound
 Super cooled liquid
 Becomes softer & loses viscosity when heated
 No specific melting point
12

13. 13

14.  CROWN GLASS
 BARIUM CROWN
GLASS
 FLINT GLASS
 HIGH INDEX
GLASS
14

15. CROWN
GLASS
FLINT
GLASS
BARIUM
CROWN
GLASS
HIGH
INDEX
GLASS
15

16.  70 % Silica , 14- 16 % sodium oxide , 11-13 %
calcium oxide and small percentage of potassium ,
borax , antimony , arsenic
 Used for single vision.
 Distant portion of bifocal, trifocal.
 Most widely used in ophthalmic industry.
16

17.  R.I - 1.523
 Abbe value - 59
 Specific gravity – 2.54
 Transparency - 91.6%
 U.V. absorption – 280 nm
17

18.  Highly scratch resistant
 Resistant to solvents & temperature fluctuation
 Tinted by vaccum coating
 Good optical qualities
 Available in photochromic sunglass option
18

19.  Low in costs
 Produce least amount of chromatic aberration
 Blanks available in all sizes
19

20.  Low impact resistance
 Heavier material
 Chips can easily form while edging & handling
 Not appropriate for children & sport wear
 U.V. absorption not 100 % (upto 280nm)
20

21.  Ingredients:-
45-65% lead oxide
25-45% silica
10% soda + potassium oxide
21

22. DENSE
FLINT
EXTRA
DENSE
FLINT
22

23. Types Refractive
index
Abbe
value
Specific
gravity
Dense flint 1.649 33.8 3.90
Extra
dense flint
1.69 30.9 4.23
23

24.  Used in kryptok bifocal
 Kryptok Lenses. Also referred to as a round lens,
the magnifying area in the lower part of the lens is
a complete circle. The lens can restrict viewing up
top, due to the round shape. There is less
significant transition between reading and distance
vision.
 High prescription
24

25.  High dispersion
 High specific gravity
 Transparency less than crown glass
25

26.  25 – 40 % barium oxide
 30 % Silica
Lime , zinc , aluminum , boron , zirconium
26

27. LIGHT
BARIUM
CROWN GLASS
DENSE
BARIUM
CROWN GLASS
27

28. Types Refractive
index
Abbe
value
Specific
gravity
Light
barium
1.573 57.4 3.21
Dense
barium
1.616 55.1 3.36
28

29.  High RI with out an appreciable increase in
chromatic dispersion
29

30.  Chromatic dispersion more than crown glass
30

31.  Any lens having Refractive
Index (RI) higher than 1.523 in
glass is called high index lens
 Available in 1.6 , 1.7 , 1.8 , &
1.9
 Contents- high % of Titanium
oxide
 Transmission- less than 92%
 Useful for reducing the
thickness for high powered
lenses
31

32.  Organic substances based on molecular frame
work of carbon with H, N, O
 Superior to glass in many aspects except their
softness
 They are comparatively more attractive
 Can be easily tinted for cosmetic appeal and sun
wear
32

33. • ZIESS
DURALATE
• HIGH INDEX
• POLY
CARBONATE
• PMMA
CR - 39 TRIVEX
TINT
POLARIZED
LENS
33

34.  It is a polymeric material of large molecular wt.
which can be shaped by flow
 Also called as organic lenses.
 Most plastics are synthetic materials formed by
combining various organic ingredients with
inorganic materials such as carbon, hydrogen,
,nitrogen, chlorine & Sulphur.
34

35. THERMOSETTING
THERMOPLASTIC
35

36.  It is also called as Columbia resin or allyl diglycol
carbonate.
 CR – 39 or allyl diglycol carbonate is a plastic
polymer commonly used in manufacture of
eyeglass lenses.
 It was developed by Pittsburgh Plate Glass
industries.
 It is the thermosetting material.
36

37.  CR stands for Columbia Resin & it is 39th
formula of a thermosetting plastic developed by
the Columbia resin project of PPG industries back
in 1940.
 “CR” stands for Columbia Resin, and the number
39 denotes the type of Columbia Resin used.
37

38.  For years CR- 39 was used without anti scratch
coating.
 Now, however, most CR-39 lenses come with an
anti scratch coating, making the material much
more scratch resistant.
 For smaller, high velocity, sharply pointed objects,
CR-39 lenses perform better than chemically
tempered glass.
38

39.  CR-39 plastic lenses do not fog up as easily as
glass lenses.
 Whereas welding or grinding spatter will pit or
permanently stick to glass lenses, it does not
adhere to plastic lens material.
39

40. 40

41.  Refractive index : 1.498
 Abbe value : 59.3
 Density : 1.31 g/cm3
 UV cutoff : 355 nm
 Specific gravity : 1.32 Gram/cc
41

42.  The material is highly impact resistant and carries
high transparency.
 Multiple tinting and coating is possible.
 only drawback is weak resistant to abrasion.
42

43. 43

44.  Lightness
 Impact resistance
 Chemical inertness
 Resistance to pitting
 Resistance to fogging
 Tintability
 Versatility in optical design
44

45.  Surface abrasion
 Warpage upon glazing
 Increased thickness
 Inferior photochromic properties
 Index variability with temperature
45

46.  Petroleum
derivative and
plastic polymer
 It is a high index
plastic lens
 Gives extra level of
protection to the
lens wearers
 Usually preferred
for children and
sportswear
46

47.  It is a synthetic material.
 Because of their unique molecular structure
they can flex easily without getting deformed.
 All polycarbonate lens absorb U.V radiation up
to 380nm without additional treatment.
 Polycarbonate lens produce more reflection
than ophthalmic crown glass.
47

48.  It was developed in the 1970s for aerospace
application, and is currently used for the helmet
visors of astronauts and for space shuttle
windshields.
 Eyeglass lenses made from polycarbonate were
introduced in the early 1980s in response to
demand for lightweight impact resistance lenses.
48

49. 49

50.  R.I. :- 1.586
 Abbe value :- 30
 Specific gravity :- 1.20
 U.V. absorption :- 380 nm
Density : 1.2 g / cm3
50

51.  Lightest of all materials
 Most impact resistance material
 30-40% thinner than CR-39
 Absorbs nearly 100% of UV-A and UV-B radiation
 Can be hard coated for scratch resistance
 Center thickness can be ground to 1.2mm
 Absorbs ultra violet radiation up to 380nm
51

52.  High chromatic aberration
 Poor optical qualities
 More scratches are formed
 Transparency is less
 More lens distortion
 Difficult to dye
 More expensive
52

53.  Very soft material – low scratch resistance
 Distortions in vision away from optical center
 Not as easy to tint – difficult to match colours
 Produces undesirable lateral chromatic aberration
upon peripheral gaze
53

54.  UV protected lenses
 Coated with fine layer of silicon
 Make scratch resistance
 CR-39 lenses is higher than heat tampered glass
lenses but equal to chemical tampered glass
lenses.
54

55.  Available in 2 forms
1) Glass high-index
2) Plastic high-index
 GHI are made up of titanium oxide, barium oxide
or lead oxide
 PHI are made up of Thermosetting plastics
 These lenses have higher than standard R.I.
 Most cosmetically acceptable lenses
 It enables the lens to bend light "faster".
 Hence they are lighter and thinner than standard
lenses.
55

56. 56

57.  Refractive index
:1.640 – 1.740
 Abbe value : 42 –
32
 Density : 1.3 – 1.5
 UV cutoff : 380 –
400 nm
57

58. Types Refractive
Index
Abbe value Specific
gravity
Glass
High
Index
1.600 36 1.45
Plastic
High
Index
1.597 37 1.34
58

59.  Good cosmesis
 Magnification is reduced
 Available in range of lens types including
photochromic , multifocal etc.
 Thinner and lighter than conventional lens
materials
 Can be multicoated , tinted ,UV etc
 Available in wide range of blank size & finished as
well as semi finished lens types
59

60.  Greater distortions away from optical centre
 Not available in larger blank sizes
 Less impact resistant
 More chromatic dispersion
 Off axis abberation are seen
 Fragile, expensive
 Incases of plus lenses, the periphery become
too thin and hence easily breakable.
 Higher RI, more the reflections, hence
reducing transmission .
60

61.  Also known as Perspex or transpex
 Also known as PMMA.
 Polymerization of metha methacrylate
 MMA its prepared by hydralysis & esterification
of acetone cyanohydrins
 Cyanohydrins produced by action of hydro cyanic
add on acetone
61

62. 62

63. 63

64.  Refractive index :- 1.49
 Velocity :- 58
Density :- 1.119
 Half of the weight of crown glass
64

65.  Also known as phoenix or triology
 Similar to polycarbonate but have higher quality
optics & thus provide clearer vision
65

66.  Refractive index : 1.532
 Abbe value : 43-45
 Density : 1.1 g / cm3
 UV cutoff : 380 nm
66

67.  Trivex is lighter in
weight than standard
plastic but not quite as
thin as polycarbonate.
 Trivex is a more rigid
material making it a
better selection for
rimless or dril mount
frames.
 Dose not break easily.
67

68.  get scratch easily
68

69.  Polarized filter is made by heating and
stretching thin sheet of PVA (poly vinyl
alcohol) to about 4 times of its original length.
 Sheet is then passed through weak & iodine
sol.
 Iodine molecules diffuse into the PVA layer
and thus creates a polarizing filter.
 This thin sheet is laminated between 2 layer of
coated cellulose acetate butyrate and then
pressed to the desired curvature.
69

70.  Available in
variety of tints.
 Metallic oxides
are added to the
molten glass
material to get
desired tints.
METAL
OXIDES
COLOU
R
Iron Green
Cobalt Blue
Gold Red
Nickel Brown
Silver Yellow
Manganese Pink
70

71. GLASS
 Solid glass tint
 Glass photo chromic tint
 Laminated tints
 Vacuum coated tints
PLASTIC
 Deep tint
 Plastic photo chromic tint
71

72.  Reduce of glare across the visible spectrum
 Protection against harmful radiations
 Improved cosmetic appearance
72

73. Glass CR-39 Polycarbonat
e
Trivex
Specific
gravit
y
2.54 1.32 1.20 1.11
R.I 1.523 1.498 1.586 1.532
Abbe
value
58.9 58 30 40
73

74. PROPERTIES
OF LENSES
74

75. 75

76. ABBE VALUE REFLECTANCE
REFRACTIVE
INDEX
ABSORPTION
76

77.  Definition :- Reciprocal of the dispersive
power of the material and gives a measure
of the material ability to hold spectrum
together
The higher the abbe value less will be the
transverse chromatic aberration at periphery
Used to calculate axial and transverse
chromatic aberration
77

78. 78

79.  Abbe number of 60 is considered to have the least
chromatic aberrations and abbe number of 30 is for
the most chromatic aberrations.
 When the wearer moves the eyes away from the
centre and looks through the periphery of the lens,
the prism is created.
79

80.  The amount of prism created together with the
dispersion value of the lens material affects the
amount of “colour fringes” the wearer sees.
 Standard plastic lenses have an abbe value of 58.
 Most high index materials have a much lower
Abbe value.
80

81.  Reflectance is the phenomenon of light reflection
occurs at each of the lens surfaces.
 The result is the loss of lens transparency and
undesirable reflections on the lens surfaces.
81

82.  The reflectance of the lens surface is calculated from
the refractive index of the material.
 When the light is normal on the lens surface, the
percentage of light reflected at each surface is given
 by:
 Reflectance = 100 (n – 1)² / (n + 1)²%
82

83.  The higher the refractive index, the greater the
proportion of light reflected from the surfaces.
83

84.  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%
84

85.  Definition :- the ratio of speed of light in a
vacuum to the speed of light in a given medium
 The higher the R.I. the thinner the lens can be
made
 If a material has a greater ability to refract
light, less curve is required to obtain a specific
power hence resulting in a thinner lens.
 Materials with an index between 1.523 and
1.57 are considered as mid-index, while 1.58
and greater is considered as high-index.
85

86.  n = Velocity of light in air
 Velocity of light in the medium
86

87.  The amount of light which goes through a lens can
be reduced because of absorption by the lens
material.
 This is negligible in case of a non–tinted lens, but
constitutes an intrinsic function of a tinted or photo
chromatic lens..
87

88.  Absorption of an ophthalmic lens generally refers
to its internal absorption, i.e. to the percentage of
light absorbed between the front and the rear lens
surfaces.
 Lens absorption occurs according to Lambert’s law
and varies exponentially as a function of lens
thickness.
88

89. SPECIFIC
GRAVITY
IMPACT
RESISTANCE
SCRATCH
RESISTANCE
89

90.  Definition :- It is the ratio of 1 cubic cm of a
material to 1 cubic cm of water
 The higher the specific gravity of a lens
material, the higher will be the density and
heavier will be the lens
 SG will give a rough idea about the relative
weight of various lens
 It cannot accurately predict relatively weights
of finished lenses as the denser material
normally have higher R.I. and thus have a
smaller mass.
90

91.  Definition :- Relatively susceptibility of
plastics to fracture under stresses applied at
high speed
 Relative impact resistance of various materials
will vary, depending on the size and shape of
the missile used in the test
 The standard test employed by FDA involves
dropping a 5/8 inch steel ball on to the lens
from a height of 50 inches
 Polycarbonate is the most impact resistance
followed by high index plastic lenses, CR-39,
and finally the ordinary glass lenses.
91

92. 92

93.  One of the straight features of glass lenses is
abrasion resistance.
 Plastic lenses need to be coated with an additional
resin to approach the scratch resistance of glasses.
 These resin coatings can be applied in a number of
ways.

93

94.  Lenses may be dipped, or a thin layer of resin may
be spun onto the Lens surface.
 These coating layers are usually 5 micron thick.
 While abrasion resistance is an important property
for spectacle lenses, it is not crucial to the normal
use of the product.
94

95.  Electrical properties characterize effects of
electromagnetic waves and electricity on the
materials.
95

96.  chemical properties shows the reaction of materials
to the chemical substances usually found during
lens manufacture, in every day life, or to certain
extreme conditions to which materials can be
subjected.
 These substances are usually hot or cold water,
acids and organic solvents.
96

97.  Thermal properties state changes of state and the
effect of temperature on materials.
97

98.  Therefore, a hypothetical ideal lens material from
both the patient’s and practitioner’s point of view – a
high refractive index with low dispersion,
unbreakable, unscratchable, low density, available
with aspherical surfaces in all multifocal form, easy
to tint and to add “inexpensive”, and from the
financial point of view, we do not really want them
last forever.
98

99.  Unfortunately, there is no lens material that fits
this description, and we have to use compromise
99

100. THANK
YOU
100