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PRESENTED BY :
• Introduction to ophthalmic lens and its
• Glass material –history and its types
• Plastic material – history and its types
• Properties of ophthalmic lenses- its
classifications and sub classification
WHAT IS OPHTHALMIC LENS ?
• It is the portion of the transparent medium
bounded by two refracting surfaces at least one
of which is curved.
• Ophthalmic lens materials means all materials
used during manufacturing, i.e. all materials
entered into the composition of the basic
• There are two types of lens material.
• Glass material often referred to as mineral
1. Absorb heat and cold
2. Are scratch resistant
3. Highest optical clarity
4. Low Aberration
HISTORY OF GLASS MATERIAL
• Early optical glasses were known as either
crown or flint glass.
• The adjective crown was originally applied to
window glass used seventeenth and
eighteenth century for houses in England.
• Before the development of optical glass the
pieces of this glass is used for ophthalmic
lenses and the lenses were known as crown
• Today Crown glass refers to glass whose
primary ingredients are silica, soda or potash
• 1676, George Ravenscorft, an Englishman,
used ground flints as a source of silica and
incorporated a relatively large quantity of lead
as one of the basic constituents of glass.
• The glass became known as Flint glass.
• It was softer, heavier, clearer and more
brilliant than any other glass available and was
used for drinking vessels, bowls and quality
• Beginning of in 1876 Ernst Abbe and Otto
Schott of Jena, Germany collaborated in
experimenting with large number of chemical
oxides in the manufacture of glass and
developed a wide range of new glasses.
• In 1880, the invention of barium crown by
Abbe introduced a glass of high index without
an appreciable increase in dispersive power.
• Today Pittsburgh Plate Glass industries and
Scott glass Technologies comprise the major
TYPES OF GLASS MATERIAL
• 70 % Silica , 14- 16 % sodium oxide , 11- 13 %
calcium oxide and small percentage of
potassium , borax , antimony , arsenic.
• Used for single vision lenses
• Most common used in ophthalmic industry
• Refractive index- 1.523
• Abbe value - 59
• Specific gravity- 2.54
• Transparency- 91.6%
• Highly scratch resistant
• Good optical qualities
• Available in single vision and multifocal lenses
• Available in photochromic sunglass option
• Low cost
• Reduce chromatic aberration
• Low impact resistance
• Heavier material
• Chips can easily form while edging
• Lead oxide 45% to 65%
• Silica 25% to 45%
• Mixture of soda and potassium oxide
• Used for bifocal segments for fused bifocals
and single vision lenses of high power because
the high index of refraction makes the lenses
• Refraction index- Light flint : 1.580
- Dense flint : 1.690
• Abbe value - 30 to 40
• Available in single vision and bifocal lenses
• Transparency less than crown glass
• Distortion of image
BARIUM CROWN GLASS
• Barium oxide 25% to 45%
• Barium oxide which has the same effect as
lead oxide in increasing refractive index but
without great increase in chromatic
• Refractive index - 1.514 to 1.616
• Abbe values - 55 to 59
HIGH INDEX GLASS
• There are higher index glass lens materials
available that will reduces thickness for higher
• Contents- High % of Titanium oxide
• Refractive index- Available in 1.6 , 1.7 , 1.8 , &
• Abbe value – 33 , 32 , 31 , 30
• Available in range of lens types including
photochromic , multifocal etc.
• Thinner than other lens materials
• Can be multicoated
• Available in wide range of blank size &
finished as well as semi finished lens types
• Greater distortions
• Not available in larger blank sizes
• Less impact resistant
• More chromatic dispersion
• Off axis aberration are seen
PLASTIC LENS MATERIAL
• It is a polymeric material of large molecular
wt. which can be shaped by flow.
• Also called as organic material.
• Most plastics are synthetic materials formed
by combining various organic ingredients with
inorganic materials such as carbon, hydrogen,
nitrogen, chlorine & Sulphur.
HISTORY OF PLASTIC MATERIAL
• 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 2 World
war were PMMA develop CR39 for use in
• In 1947 Robert Graham formed Armorlite lens
company in California later described the first
ophthalmic lens made from CR39.
• In 1957 General Electric developed a new
plastic material a Polycarbonate called Lexan.
• In 1982 Corning glass work the development
of a lens called Corlon.
TYPES OF PLASTIC MATERIAL
• It is also called as Columbia resin or allyl
• CR – 39 or allyl diglycol carbonate is a plastic
polymer commonly used in manufacture of
• It was developed by (PPG) Pittsburgh Plate
• 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 39th 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.
• CR-39 plastic lenses do not fog up as easily as
• Refractive index - 1.498
• Abbe value - 58
• Specific gravity - 1.32
• Lighter weight than glass lenses
• Impact resistance
• Resistance of fogging
• Can yellow with age
• Scratches more easily
• Surface abrasion
• Polycarbonate is a thermoplastic.
• The lens material is soft and requires an anti-
• It was developed in the 1970s for aerospace
application, and is currently used for the
helmet visors of astronauts and for space
• Eyeglass lenses made from polycarbonate
were introduced in the early 1980s in
response to demand for lightweight impact
• Refractive index- 1.586
• Abbe value- 29
• Specific gravity- 1.20
• Lightest of all material
• Most impact resistant material
• 30-40% thinner than CR39
• Absorb 100% UV rays
• High chromatic aberration
• More scratches and more epensive
• Transparency less
HIGH INDEX PLASTIC
• Plastic are made up of Thermosetting plastics.
• These lenses have higher than standard
• Most cosmetically acceptable lenses.
• It enable the lens to bend light “faster” than
• Hence they are lighter and thinner than
• Refractive index – 1.66
• Abbe value – 32
• Density – 1.35
• Cosmetically good
• Magnification is reduced
• Thinner and lighter than other lenses
• Available in range of lens type including
photochromatic , multifocal etc
• Impact resistant
• Greater distortion
• Not available in larger blank size
• More chromatic dispersion
• Off axis aberration are seen
• Trivex lenses developed by PPG industries.
• The lens material was originally for military
• The lens material to provide excellent safety
for window in combat vehicles and good
• Similar to polycarbonate but have higher
quality optics & thus provide clearer vision.
• Refractive index – 1.523
• Abbe value – 35 to 43
• Density – 1.11
• Impact resistance
• Lighter in weight
• More scrach
PROPERTIES OF LENSES
ABBE VALUE REFLECTANCE
• DEFINITION : Reciprocal of the dispersive
power of the material and gives a measure of
the material ability to transmit the light.
• Abbe number of 60 is considered to have the
least chromatic aberrations and Abbe number
of 30 is for the most chromatic aberrations.
• Most high index materials have a much lower
• 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.
• The reflectance of the lens surface is
calculated from the refractive index of the
DEFINITION : The ratio of speed of light in a
vacuum to the speed of light in a given
• The higher the R.I. the thinner the lens can be
• 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.
• 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 function of a tinted or
photo chromatic lens.
DEFINITION : The ratio of the density of a
substance to the density of some substance
(such as pure water) taken as a standard when
both densities are obtained by weighing of air.
• Which tell us about the relative weight of the
material with respect to same amount of
• The higher the specific gravity of a lens
material, the higher will be the density and
heavier will be the lens.
DEFINITION : is the ability of a material
withstand a high force or shock applied to it
over a short period of time.
• Relative impact resistance of various materials
will vary, depending on the size and shape of
the missile used in the test.
• Polycarbonate is the most impact resistance
• Lenses that are treated front and back surface
with a clear, scratch resistance coating have a
much harder surface that is more resistance to
• Front and back surface features of glass lenses
is scratch (abrasion) resistance.
• Plastic lenses need to be coated with an
additional resin to approach the scratch
resistance of glasses.
• Electrical properties characterize effects of
electromagnetic waves and electricity on the
• Chemical properties shows the reaction of
materials to the chemical substances usually
found during lens manufacture, andin every
• These substances are usually hot or cold
water, acids and organic solvents.
• Thermal properties changes of state and the
effect of temperature on materials.
• System for ophthalmic Dispensing
Clifford W. Brooks and Irvin M. Borish