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LENS MATERIAL &
MADE BY : SWATI PANARA
FROM : BHARTIMAIYA
COLLEGE OF OPTOMETRY
2nd YEAR 3rd SEMESTER
What is an Ophthalmic Lens ?
It is the portion of the transparent medium
bounded by 2 refracting surfaces at least 1
of which is curved.
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
Quartz or rock made out of pure silica was
Its hardness and low mist retaining
property made it ideal for spectacle lens
Not used in optical instruments since it is
doubly refracting material
Where are they today?
Clear natural crystals
of quartz are very
rare to find
So their use is almost
comparisons between glass &
Glass lenses Plastic lenses
Low impact resistant
3 piece can’t be use
Not proffered for children
High impact resistant
Highly Scratch resistant
3 piece can be use
good proffered for children
Glass lenses Plastic lenses
Aberration is low
Higher tendency to fog
It not necessary required
2% greater transmission
Aberration is high
Lower tendency to fog
must necessary required
GLASS LENS MATERIAL
Super cooled liquid
Becomes softer & loses viscosity when
No specific melting point
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.
Highly scratch resistant
Resistant to solvents & temperature
Tinted by vaccum coating
Good optical qualities
High range curves blanks & addition
Available in photochromic sunglass option 14
Low in costs
Produce least amount of chromatic aberration
Blanks available in all sizes
Low impact resistance
Chips can easily form while edging &
Not appropriate for children & sport wear
U.V. absorption not 100 % (upto 280nm)
45-65% lead oxide
10% soda + potassium oxide
1.573 57.4 3.21
1.616 55.1 3.36
High RI with out an appreciable increase in
Chromatic dispersion more than crown
HIGH INDEX GLASS
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 , &
Contents- high % of Titanium
Transmission- less than 92%
Useful for reducing the
thickness for high powered
PLASTIC LENS MATERIAL
Organic substances based on molecular
frame work of carbon with H, N, O
Superior to glass in many aspects except
They are comparatively more attractive
Can be easily tinted for cosmetic appeal
and sun wear
• HIGH INDEX
CR - 39 TRIVEX
PLASTIC LENS MATERIAL
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 &
PLASTIC LENS MATERIAL
CR - 39
It is also called as Columbia resin or allyl
CR – 39 or allyl diglycol carbonate is a
plastic polymer commonly used in
manufacture of eyeglass lenses.
It was developed by Pittsburgh Plate Glass
It is the thermosetting material.
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
For years CR- 39 was used without anti
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.
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.
Resistance to pitting
Resistance to fogging
Versatility in optical design
Warpage upon glazing
Inferior photochromic properties
Index variability with temperature
It is a high index
Gives extra level of
protection to the
for children and
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.
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
R.I. :- 1.586
Abbe value :- 30
Specific gravity :- 1.20
U.V. absorption :- 380 nm
Density : 1.2 g / cm3
Lightest of all materials
Most impact resistance material
30-40% thinner than CR-39
Absorbs nearly 100% of UV-A and UV-B
Can be hard coated for scratch resistance
Center thickness can be ground to 1.2mm
Absorbs ultra violet radiation up to 380nm 47
High chromatic aberration
Poor optical qualities
More scratches are formed
Transparency is less
More lens distortion
Difficult to dye
Very soft material – low scratch resistance
Distortions in vision away from optical
Not as easy to tint – difficult to match
Produces undesirable lateral chromatic
aberration upon peripheral gaze
ZIESS DURALATE LENSES
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.
Available in 2 forms
1) Glass high-index
2) Plastic high-index
GHI are made up of titanium oxide, barium oxide or
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
High index plastics
:1.640 – 1.740
Abbe value : 42 –
Density : 1.3 – 1.5
UV cutoff : 380 –
Abbe value Specific
1.600 36 1.45
1.597 37 1.34
Magnification is reduced
Available in range of lens types including
photochromic , multifocal etc.
Thinner and lighter than conventional lens
Can be multicoated , tinted ,UV etc
Available in wide range of blank size &
finished as well as semi finished lens types 55
Greater distortions away from optical centre
Not available in larger blank sizes
Less impact resistant
More chromatic dispersion
Off axis abberation are seen
Incases of plus lenses, the periphery become too
thin and hence easily breakable.
Higher RI, more the reflections, hence reducing
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
Properties of PMMA
Refractive index :- 1.49
Velocity :- 58
Density :- 1.119
Half of the weight of crown glass
Also known as phoenix or triology
Similar to polycarbonate but have higher
quality optics & thus provide clearer vision
Refractive index : 1.532
Abbe value : 43-45
Density : 1.1 g / cm3
UV cutoff : 380 nm
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
Dose not break easily. 63
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.
variety of tints.
are added to
to get desired
Manganese Pink 66
A tinted lens could be available in:-
Solid glass tint
Glass photo chromic tint
Vacuum coated tints
Plastic photo chromic tint
Reduce of glare across the visible spectrum
Protection against harmful radiations
Improved cosmetic appearance
Glass CR-39 Polycarbonat
2.54 1.32 1.20 1.11
R.I 1.523 1.498 1.586 1.532
58.9 58 30 40
ABBE VALUE REFLECTANCE
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
Abbe number of 60 is considered to have
the least chromatic aberrations and abbe
number of 30 is for the most chromatic
When the wearer moves the eyes away
from the centre and looks through the
periphery of the lens, the prism is created.
The amount of prism created together with
the dispersion value of the lens material
affects the amount of “colour fringes” the
Standard plastic lenses have an abbe value
Most high index materials have a much
lower Abbe value.
Reflectance is the phenomenon of light
reflection occurs at each of the lens
The result is the loss of lens transparency
and undesirable reflections on the lens
The reflectance of the lens surface is
calculated from the refractive index of the
When the light is normal on the lens
surface, the percentage of light reflected at
each surface is given
Reflectance = 100 (n – 1)² / (n + 1)²%
The higher the refractive index, the greater
the proportion of light reflected from the
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
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.
n = Velocity of light in air
Velocity of light in the medium
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..
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.
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
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.
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.
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.
Lenses may be dipped, or a thin layer of
resin may be spun onto the Lens surface.
These coating layers are usually 5 micron
While abrasion resistance is an important
property for spectacle lenses, it is not
crucial to the normal use of the product.
Electrical properties characterize effects of
electromagnetic waves and electricity on
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
These substances are usually hot or cold
water, acids and organic solvents.
Thermal properties state changes of state
and the effect of temperature on materials.
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
Unfortunately, there is no lens material that
fits this description, and we have to use