Published on 02/01/2019

1. LENS MATERIALS
PRESENTED BY :
SHOAIB AKHTAR

2. OBJECTIVE
• Introduction to ophthalmic lens and its
material
• Glass material –history and its types
• Plastic material – history and its types
• Properties of ophthalmic lenses- its
classifications and sub classification

3. WHAT IS OPHTHALMIC LENS ?
• It is the portion of the transparent medium
bounded by two refracting surfaces at least one
of which is curved.

4. LENS MATERIAL
• Ophthalmic lens materials means all materials
used during manufacturing, i.e. all materials
entered into the composition of the basic
ophthalmic lens.
• There are two types of lens material.
(1) Glass
(2) Plastic

5. GLASS MATERIAL
• Glass material often referred to as mineral
lenses.
 Advantages
1. Absorb heat and cold
2. Are scratch resistant
3. Highest optical clarity
4. Low Aberration

6. 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
lenses.

7. Cont...
• Today Crown glass refers to glass whose
primary ingredients are silica, soda or potash
and lime.
• 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.

8. Cont...
• It was softer, heavier, clearer and more
brilliant than any other glass available and was
used for drinking vessels, bowls and quality
crystal wear.
• 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.

9. Cont...
• 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
glass manufacture.

10. CROWN FLINT
GLASS GLASS
BARIUM HIGH
CROWN INDEX
GLASS GLASS
10
TYPES OF GLASS MATERIAL

11. CROWN GLASS
• 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

12. Cont...
• Refractive index- 1.523
• Abbe value - 59
• Specific gravity- 2.54
• Transparency- 91.6%

13. Cont...
 Advantages
• Highly scratch resistant
• Good optical qualities
• Available in single vision and multifocal lenses
• Available in photochromic sunglass option
• Low cost
• Reduce chromatic aberration

14. Cont...
 Disadvantages
• Low impact resistance
• Heavier material
• Chips can easily form while edging

15. FLINT GLASS
• 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
thinner.

16. Cont...
• Refraction index- Light flint : 1.580
- Dense flint : 1.690
• Abbe value - 30 to 40
 Advantages
• Available in single vision and bifocal lenses
 Disadvantages
• Transparency less than crown glass
• Distortion of image

17. 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
dispersion.
• Refractive index - 1.514 to 1.616
• Abbe values - 55 to 59

18. HIGH INDEX GLASS
• There are higher index glass lens materials
available that will reduces thickness for higher
powered lenses.
• Contents- High % of Titanium oxide
• Refractive index- Available in 1.6 , 1.7 , 1.8 , &
1.9
• Abbe value – 33 , 32 , 31 , 30

19. Cont...

20. Cont...
 Advantages
• 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

21. Cont...
 Disadvantages
• Greater distortions
• Not available in larger blank sizes
• Less impact resistant
• More chromatic dispersion
• Off axis aberration are seen

22. 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.

23. 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
military aircraft.
• In 1947 Robert Graham formed Armorlite lens
company in California later described the first
ophthalmic lens made from CR39.

24. Cont...
• 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.

25. CR39 POLYCAR
BONATE
TRIVEX HIGH
LENSES INDEX
PLASTIC
25
TYPES OF PLASTIC MATERIAL

26. Cont...

27. CR39
• 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
eye lenses.
• It was developed by (PPG) Pittsburgh Plate
Glass industries.
• It is the thermosetting material.

28. Cont...
• 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
Resin used.
• For years CR- 39 was used without anti
scratch coating.

29. Cont...
• 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.

30. Cont...
• Refractive index - 1.498
• Abbe value - 58
• Specific gravity - 1.32
 Advantages
• Lighter weight than glass lenses
• Impact resistance
• Resistance of fogging

31. Cont...
Disadvantages
• Can yellow with age
• Scratches more easily
• Surface abrasion

32. POLYCARBONATE
• Polycarbonate is a thermoplastic.
• The lens material is soft and requires an anti-
scratch coating.
• It was developed in the 1970s for aerospace
application, and is currently used for the
helmet visors of astronauts and for space
shuttle windshields.

33. Cont...
• Eyeglass lenses made from polycarbonate
were introduced in the early 1980s in
response to demand for lightweight impact
resistance lenses.
• Refractive index- 1.586
• Abbe value- 29
• Specific gravity- 1.20

34. Cont...
 Advantages
• Lightest of all material
• Most impact resistant material
• 30-40% thinner than CR39
• Absorb 100% UV rays
Disadvantages
• High chromatic aberration
• More scratches and more epensive
• Transparency less

35. HIGH INDEX PLASTIC
• Plastic are made up of Thermosetting plastics.
• These lenses have higher than standard
refractive index.
• Most cosmetically acceptable lenses.
• It enable the lens to bend light “faster” than
other.
• Hence they are lighter and thinner than
standard lenses.

36. Cont...
• Refractive index – 1.66
• Abbe value – 32
• Density – 1.35
Advantages
• Cosmetically good
• Magnification is reduced
• Thinner and lighter than other lenses

37. Cont...
• Available in range of lens type including
photochromatic , multifocal etc
• Impact resistant
Disadvantages
• Greater distortion
• Not available in larger blank size
• More chromatic dispersion
• Off axis aberration are seen
• Expensive

38. TRIVEX LENSES
• Trivex lenses developed by PPG industries.
• 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.

39. Cont...
• Refractive index – 1.523
• Abbe value – 35 to 43
• Density – 1.11
Advantages
• Impact resistance
• Lighter in weight
Disadvantages
• More scrach

40. PROPERTIES OF LENSES

41. OPTICAL PROPERTIES
41
ABBE VALUE REFLECTANCE
REFRACTIVE
INDEX
ABSORPTION

42. ABBE VALUE
• 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
Abbe value.

43. REFLECTANCE
• 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
material.

44. REFRACTIVE INDEX
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.
• 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.

45. ABSORPTION
• 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.

46. MECHANICAL PROPERTIES
46
SPECIFIC
GRAVITY
IMPACT
RESISTANCE
SCRATCH
RESISTANCE

47. SPECIFIC GRAVITY
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
water.
• The higher the specific gravity of a lens
material, the higher will be the density and
heavier will be the lens.

48. IMPACT RESISTANCE
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
material.

49. Cont...

50. SCRATCH 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
scratching.
• 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.

51. Cont...

52. ELECTRICAL PROPERTIES
• Electrical properties characterize effects of
electromagnetic waves and electricity on the
materials.

53. CHEMICAL PROPERTIES
• Chemical properties shows the reaction of
materials to the chemical substances usually
found during lens manufacture, andin every
day life.
• These substances are usually hot or cold
water, acids and organic solvents.

54. THERMAL PROPERTIES
• Thermal properties changes of state and the
effect of temperature on materials.

55. REFERENCE
• System for ophthalmic Dispensing
Clifford W. Brooks and Irvin M. Borish
• Internet

56. THANK YOU