Contact lens materials and solutions

1. CONTACT LENS
MATERIALS AND SOLUTIONS
Dr.P.Neha kamalini,
M.S.Ophthalmology,
Guntur medical college

2. ▪Contact lens is an artificial device whose front
surface substitutes the anterior surface of the
cornea.

3. HISTORY OF CONTACT LENSES (CL)
▪In 1508, LEONARDO DA
VINCI sketched the first
forms of new refracted
surface on the cornea.

4. He used the example of a very large glass bowl filled with
water
immersion of the eyes in water theoretically corrected vision.
H2O

5. In 1636, DESCARTES
suggested applying a tube full
of water directly to the eye to
correct a refractive error.

6. Optical apparatus described by descartes
H2O

7. In 1887, ADOLF FICK was apparently the first to
successfully fit contact lenses, which were made from
blown glass shells

8. FA MÜLLER and SONS (1887)
• Artificial eye makers in Germany
• Made lenses from blown glass

9. OWICHTERLE & D LIM
Introduced soft contact lens made
of
hydroxyethylmethacrylate(HEMA)
in 1961

10. CLASSIFICATION – NATURE OF MATERIAL
1. Rigid non-gas permeable Contact
lenses(PMMA)
2. Rigid gas permeable contact lenses(CAB)
3. Soft contact lenses(HEMA)

14. CONTACT LENS MATERIALS

15. Nomenclature of material properties
WETTABILITY:
• Adherence of a liquid to the surface of a solid

16. OXYGEN PERMEABILITY
• Property of polymeric material to transmit oxygen
• Expressed as : coefficient of variable Dk
D represents diffusion
k represents solubility
• The higher the Dk, the more permeable the
material.

17. OXYGEN TRANSMISSIBILITY
• The total oxygen transmissibility of the lens is
denoted by Dk/t or Dk/L
t (or L) is the thickness
• thicker : the oxygen transmissibility is reduced.
• thinner : the transmissibility is increased.

18. IDEAL MATERIAL
▪BIOCOMPATIBILITY- should not be harmful
▪OPTICAL PROPERTIES- transparent
▪GAS PERMEABILITY – freely gas permeable
▪TOLERANCE – gas permeability and design.

19. ▪MOULDING – amenable to easy shaping and
manufacture
▪STERILITY- resistant to contamination or
easily sterilizable
▪STABILITY - in all dimensions
▪SURFACE CHEMISTRY - easily wettable

20. RIGID NON-GAS PERMEABLE LENS
MATERIALS
▪ Manufactured from plastic or thermoplastic
material.
▪ First commercially available plastic contact lens
material was PMMA
▪ Derivative of Acrylic acid – also called acrylic.

21. Polymethyl methacrylate (PMMA)
▪ Has high optical clarity and stability
▪ Good moulding and machinability - easy to
manufacture
▪ Pure PMMA - non toxic
▪ Good wettability and durability.

22. Disadvantages
▪Impermeable to oxygen
▪Hard – cause corneal abrasions

23. RIGID GAS-PERMEABLE (RGP) LENS
MATERIALS
▪A rigid gas permeable lens is made of a
material with a molecular structure that
permits the passage of oxygen but contains no
water
▪Semisoft lenses

24. EARLIER
CELLULOSE
ACETATE BUTYRATE
(CAB)
SILICONE
STYRENE
SILICONE
ACRYLATES
(SAS)
FLUOROPOLY
MERS
PRESENT

25. Cellulose Acetate Butyrate (CAB)
▪1st widely used gas permeable rigid contact
lens material
▪Derived from wood cellulose

26. Advantages of CAB
• Good wettability.
▪ Does not attract
protein.
• Relatively inert.
• Low breakage rate.
• Very low incidence of
CLIPC.
• Relatively good for 3
and 9 o'clock staining.
Disadvantages of CAB
• Low Dk.
• Moulding necessary for
dimensional stability.
• Attracts lipids from the
tears
• Scratches easily.
• Corneal adhesion in some
cases.

27. Silicone
Advantages
▪ High oxygen
permeability
Disadvantages
▪ Hydrophobicity : poor wetting
qualities and
▪ a propensity toward attracting
deposits.
▪ softness reduces dimensional
stability and makes the lenses
prone to warpage and flexure

28. Styrene
Advantages
▪High oxygen
permeability
Disadvantages
▪Brittleness
▪Surface durability
problems

29. SILICONE
ACRYLATES
(SAS)
FLUOROPOLY
MERS
PRESENT

30. Silicone
▪Silicone gives the
polymer oxygen
permeability
▪Oxygen relies on
diffusion to move
through the voids in
the material
Fluorine
▪ Fluorine adds oxygen
permeability and
deposit resistance to
the polymer.
▪ Solubility is the
additional mechanism
by which oxygen
permeates through
fluorinated polymers.

31. Silicone acrylate
▪Silicon acrylates are copolymers in varying
proportions of acrylate (PMMA) and silicon.
Silicone - oxygen permeability
Acrylate - rigidity

32. ▪cross-linking agents are included to improve
the strength of the material
▪wetting agents such as methacrylic acid to
improve the naturally hydrophobic properties
of silicon.

33. Advantages
• Low to medium Dks
available.
• Good dimensional
stability.
• Good vision with limited
lens flexure.
• Good scratch resistance.
Disadvantages
• Attract protein from the
tears.
• Some materials are
brittle with a breakage
problem.
• High incidence of 3 and 9
o'clock staining.
• Some incidence of CLIPC.

34. Fluorosilicone acrylates (FSAs)
▪Fluorosilicone acrylates (FSAs) are the first-
choice materials for many practitioners.
▪FSA lenses : better deposit resistance
higher oxygen permeability, and
more stability than SA lenses.

35. ▪The surface haze seen on SA lenses is much
less common with FSA lenses.
▪The surface of an FSA lens can be polished
better, and the more polished surface gives
the lens better deposit resistance and
subsequently less surface haze.

36. Glycocalyx formation:
▪ The fluorine component has an inherent affinity for
mucus.
▪ This mucus affinity forms a glycocalyx around the lens
and increases comfort.
▪ Clinically, the time before dehydration and tear
breakup time are lengthened.
▪ As a result, the adaptation times of FSA lenses are
shorter than those of SA lenses.

37. Advantages
•Very high Dks possible.
•Fewer deposit
problems.
•Better wettability.
•Suitable for flexible
extended wear.
• Lower incidence of
CLIPC.
Disadvantages
• Brittle if too thin.
•Require careful
manufacture.
•Dimensional stability
depends on material and
manufacture.
•Corneal adhesion in some
cases.

38. Fluorocarbon
▪ materials are composed of fluorine and MMA to
create a polyperfluoroether.
▪ N-vinyl pyrrolidone is added for better wetting.
▪ The much larger amounts of fluorine produce a
rather high Dk/t of around 100.
▪ The high fluorine content (40–50%) makes the
lens flexible like a soft lens.

39. SOFT CONTACT LENS MATERIALS
▪ Made from hydrogels
▪ Hydrogels contain a hydrophilic group such as
hydroxyl group
▪ Hydrogels are crosslinked polymers and have a
coherent three dimensional polymeric network and
can imbibe large quantities of water without
dissolution
▪ Not dimensionally stable and swells to form labile soft
lens

40. Advantages
▪adaptation time is short due to minimal
movement and less tearing
▪suitable for long or short wearing times
▪relatively inexpensive
▪cause minimal corneal distortion
▪large optic zone makes for minimal flare
▪good for sporting activities, since they are
rarely dislodged

41. ▪Hydroxyethylmethacrylate
▪Methacrylic acid
▪N-vinyl pyrrolidone
▪Methyl methacrylate
▪Acrylamide
▪Glycerylmethylmethacrylate

42. Hydroxyethylmethacrylate
▪ was the first soft contact lens material
▪ hydrophilic because it contains a free hydroxyl group
that can bond with water.
▪ lens water content is 38%.
▪ As the polymer hydrates, or plasticizes, spaces called
pores within the lens enlarge and fill with water, and
water-soluble substances are allowed in and out of
the pores.
▪ Higher-water-content lenses have larger pores.

43. Disadvantages
▪fragility
▪easy soilage
▪difficult handling when used in low minus
prescriptions
▪low Dk
▪bacterial adherence
▪discoloration
▪Compromise of vision in astigmatic patients

44. Methacrylic acid
▪is an organic acid that increases water content
in a soft lens polymer.
▪MA is commonly seen in rigid gas-permeable
materials as a wetting agent.

45. ▪ N-vinyl pyrrolidone (NVP) is a hydrophilic
monomer.
▪ It can be used separately or together with HEMA
to form a soft lens copolymer.
▪ When combined with another hydrophilic
monomer such as HEMA or MA, it increases the
water content of the material.
▪ NVP has a carboxyl group that binds water with
even greater attraction than MA or HEMA

46. Methyl methacrylate (MMA) adds strength and
rigidity to the lens.
▪It is derived from polymethyl methacrylate
Acrylamide also adds water content to lenses.
▪it contains a carboxyl group that attracts
water.
Ethylene glycol dimethacrylate is a cross-linking
agent commonly used in contact lens materials.

47. CLASSIFICATION
HEMA-based contact
lens materials
Non–HEMA-based
materials

48. HEMA-based contact lens materials
1. HEMA lenses
2. HEMA lenses with copolymers are used to
increase water content past 38%.
HEMA and NVP
HEMA, NVP, and MMA
HEMA and MMA
HEMA and acrylamide
HEMA and MA
HEMA, NVP, and MA

49. Non–HEMA-based materials
▪are usually based on vinyl pyrrolidone
1. NVP and MMA
2. Glycerylmethylmethacrylate (GMA)

50. NVP and MMA
▪NVP : higher (70%) water content
▪MMA : rigidity.

51. Glycerylmethylmethacrylate (GMA)
▪Glyceryl : hydrophilicity because each
molecule has two hydroxyl groups.
▪MMA : rigidity.
▪The MMA monomer imparts better optics
than are found in HEMA lenses.
▪GMA has a small pore size, which makes for
better deposit resistance.

52. Soft lens groupings
FDA CLASSIFICATION
Group I low-water, nonionic polymers.
Group II high-water, nonionic polymers.
Group III low-water ionic polymers
Group IV high-water ionic polymers.

53. Ionic Materials
▪Net negative charge on surface
Non-Ionic Materials
▪Still have charged sites within polymer
matrix
▪ no net surface charge

55. CONTACT LENS SOLUTIONS

56. FUNCTIONS
• To prevent/minimize deposits
• To maintain hydration and wettability
• To provide comfort and clear vision
• To prevent or reduce the risk of ocular
infection/inflammation

57. SOLUTIONS
1. Wetting
2. Cleaning
3. Storage(soaking)
4. Rewetting agents

58. 1.WETTING AGENTS
▪Coats CL uniformly with a thin film
▪Decreases friction of CL against palpebral
conjunctiva and cornea
▪Buffer or cushioning agent- brief period

59. ESSENTIAL CHARACTERISTICS
▪Wet thoroughly
▪Hydrophilic
▪Non-irritating
▪Cleaning and antiseptic action, self-
preservative
▪No residue on lens

60. Commonly used
▪Polyvinyl alcohol
▪Polyvinyl pyrrolidone
▪Polysorbate 80
▪Polyethylene oxide
▪Cellulose like derivatives

61. 2.CLEANING SOLUTIONS
▪Detergent action
▪Bactericidal agent
Types:
▪SURFACTANT CLEANERS
▪ENZYME CLEANERS

62. Surfactant cleaners
▪ Non-ionic surfactants
▪ Debulking of protien and debris on surface
▪ Emulsify lipids
▪ Solubilize debris
▪ Removal of accumulated contaminants
▪ Daily surfactant cleaning - recommended
▪ All types of lens
▪ No direct instillation into eye.(strong conc.)

63. Daily cleaner function
63
▪To remove
 loosely bound foreign
matter, cell debris, mucus,
lipid, protein, cosmetic or
other surface contaminants

64. Recommended technique
▪Wash hands and Place lens in
palm of hand (2-3 drops of
cleaner on each lens surface )
▪Rub with forefinger (15/side)
‘To’ & ‘fro’ action or L-R action
▪Roll forefinger in both directions
clean lens periphery
▪Rinse well
64

65. ▪Avoid
vigorous rubbing
excessive pressure on lens
prolonged cleaning with abrasive cleaner
65

66. ENZYMATIC CLEANERS
(Protein removers)
•Aids in removing /loosening
tightly bound protein deposits
•Enzymes-
papain,subtilisin,pronase &
pancreatin, lipase
•Weekly done
•Lenses should be cleaned &
rinsed after enzymatic treatment
66

67. 3.SOAKING SOLUTIONS/ CONDITIONING AGENTS
▪Antiseptic Storage medium
▪Maintains lens in hydrated state
▪coating on the contact lens that protects it from
getting dirty and keeps it comfortable.

68. 4.REWETTING AGENTS
▪Wets CL while it is on cornea
▪Polyvinyl alcohol
▪methyl cellulose

69. Commonly used agents in various solutions
Benzalkonium chloride (0.004-0.01%)
▪Cationic,surface active,quaternary
ammonium germicidal agent
▪Cotton fibres render it inactive
▪EDTA- enhance anti-bacterial prop
▪Chlorbutanol- synergistic with BAC.

70. ▪Thiomersal (0.04%)-
danger of sensitization
slow rate of killing organisms
▪Chlorhexidine-
storage + disinfection,
Soft CL- 2yrs
Intolerance - Disadvantage

71. Polyvinyl alcohol-
▪Provides good adhesiveness
EDTA-
▪ Inactivates metals in solution
▪ Prevents discolouration

72. H2O2 based disinfection
▪oxidative reaction
▪hydrogen peroxide molecule
breaks down into free radicals
▪disrupts the cell wall of the
microorganisms.
▪platinum, Na.pyruvate, Na.
thiosulphate or catalase
convert peroxide into water
and oxygen.
72

73. H2O2 based disinfection
• Minim 3 hrs in 3% H2O2 recommended
- bacteria 10-15 mins
- fungi 1 hr
- acanthamoeba 3-6 hrs
• Suitable for all lens type
• Neutralizing agents
-sodium pyruvate
-sodium sulphite
-sodium thiosulphate
73

76. Lens storage & cases
▪CL stored in
-a clean CL storage case
-fresh disinfecting soln
76

77. precautions
▪Clean and change the solution in the case
daily
▪Keep the contact lenses either in the eyes or
in the lens case

78. ▪ Minimize contact with water
▪Remove lenses before swimming or using a hot tub.
▪ Contact lenses should not be rinsed with or stored in
water (tap water).
▪Lens cases should be rinsed with solution, not tap water

79. ▪AVOID contact with hair spray or other
cosmetic aerosols
▪Avoid Long and Dirty Nails
• Lenses are to be removed before going to
sleep

80. THANK YOU

81. References
▪Contact lens in ophthalmic practice-
Mark j.Mannis
▪Contact lens – Milton M.Hom