1. CONTACT LENSES

2. OPHTHALMIC APPLICATIONS
Requirements:
Good transmission of visible light
High oxygen permeability
No blood vessels
Tear-film wettability (for comfort)
Non-irritating
Resistance to bacterial/lipid/mucus adhesion
Chemical stability
UV-blockers
Ease of manufacturing and cost
Ease of cleaning and disinfection
Pigments (esthetics)
Neither hydrophilic nor hydrophobic
Surface properties
Bulk properties
Thickness
Morphology
The principal properties sought in contact lens materials, in
addition to the required optical properties, chemical stability,
and amenability to manufacture at reasonable cost, are high
oxygen transmissibility (to meet the metabolic requirements of
the cornea), tear-film wettability (for comfort), and resistance
to accumulation on the lens surfaces of mucus/protein/lipid
deposits from the tear film and other external sources. Contact
lenses also must be easy to clean and disinfect (Kastl, 1995).

3. Oxygen permeability POLYMER: The oxygen permeability coefficient, P
P = Dk,
D : diffusivity, cm2/sec
k : Henry’s law solubility coefficient, cm3(O2STP)/[cm3 (polymer) mm HG}
CONTACT LENS:
oxygen transmissibility (Dk/L) is more important than
oxygen permeability coefficient of the material/average thickness of the lens (L, in cm)

4. Red eye Lipid deposition in the form of a heavy film on the lens
surface of a silicone-hydrogel lens.
Red eye
Contact Lens and Anterior Eye (Supplement), 20, pp. S,5~10, 1997

5. RIGID CONTACT LENSES More durable
Less comfortable, longer adaptation period
Fit loosely and move as one blinks
Mechanically should tolerate the flex upon blinking
PMMA
First manufactured by Kevin Tuohey in 1948
lacks good oxygen permeability
Small and floating

7. Rigid Gas Permeable Contact lenses (RGP)
Oxygen permeable ones (RGD):
Copolymers with siloxanyl methacrylates (hydrophobic for oxygen) and methacrylic acid (hydrophilic for wetting)
+ crosslinking agents :flexibility, stiffness and durability
1970s at Polycon Laboratories
TRIS
Oxygen permeability inversely proportional to density!

8. High-Dk Silicone Hydrogels
decreases water content
İncreases permeability
oxygen is far more soluble in silicone than in water
A theoretic 100 percent water lens' Dk could be no more than 80.
highest practical water content for any material is about 80 percent, maximum permeability is approximately 40 Dk.
High Dk RGP Contact lenses could have Dk > 100.

9. Rigid Gas Permeable Contact lenses (RGP)
Perflurinated
Perfluoroalkyl–siloxanylalkyl–methyl methacrylate
hexafluroisopropylmethacrylate
high oxygen permeability
better surface properties
but their Dk is not directly related to their density like that of the original RGP
7 ay wear

10. Rigid Gas Permeable Contact lenses (RGP)
3. Cellulose acetate butyrate (CAB)
low oxygen
low scratch resistance
tends to wrap with humidity changes.

11. RGP Contact lenses
4. Siloxanyl alkylmethacrylates with styrene derivatives (Menicon)
high enough oxygen transmissibility for extended wear (2002).
Menicon SFP (Dk 134 to 138)
Menicon Z (Dk 160 to 175).
Advertised as hyper Dk lenses
No microbial keratatis

12. Suffix GAME
"filcon" (hydrophilic) for hydrogel materials
"focon" (hydrophobic) for GP materials
polymacon is the generic name of the original HEMA material

13. RGP Soft contact more expensive than RGP lenses more break in time
less durable
more replacements
more likely to get eye infections
Maintenance may require several cleaning and storing sterilization chemicals.
more break in time
Less comfortable
if you discontinue wearing for a few days, it may be difficult to become used to wearing them again.
Comfort over time: wear your lenses all the time.
Hard Plastic Lenses (PMMA)
Hard Plastic (PMMA) lenses do not allow oxygen to pass through to the cornea. They require a long adjustment period, and cannot be worn for more than 12 hours. These high-maintenance lenses were the first contact lenses on the market, but are now considered obsolete and are rarely used.

15. SOFT HYDROGEL CONTACT LENSES FDA classifications
Homogeneous hydrogels
Poly(HEMA) based
Heterogeneous hydrogels
Hydrophobic siloxane-hydrogel
High oxygen permeability

16. Homogenous Soft Hydrogel Contact lenses
Supple / Fit snugly to corneal surface
Slightly crosslinked p(HEMA)
40% water by weight
Oxygen permeability increases
Exponentially with the water content
With decreasing thickness
Otto Wichterle in 1961.
Little tear exchange
O2 should pass through the lens
The original
hydrogel contact lens material was poly(2-hydroxyethyl
methacrylate) (PHEMA) (Wichterle and Lim, 1960); at equilibrium
swelling in physiological saline solution it contains
about 40% water of hydration. (Hydration of hydrogel contact
lenses is customarily given as a percentage of water by weight,
on a wet basis.)
The soft hydrogel contact lenses (SCL) are supple and
fit snugly on the corneal surface. Because there is little tear
exchange under these lenses, most of the oxygen that reaches
the cornea must permeate through the lens. The oxygen permeability
coefficient of the standard hydrogel materials increases

18. Monomers in Contact lense Chemistry
Methylmethacrylate (MMA), which contributes hardness and strength
Silicone (SI), which increases flexibility and gas permeability through the material's silicon-oxygen bonds but has the disadvantage of poor wettability
Fluorine (FL), which also adds a smaller degree of gas permeability and improves wettability and deposit resistance in silicone-containing lenses
Hydroxyethyl-methacrylate (HEMA), the basic water-absorbing monomer of most soft lenses
Methacrylic acid (MAA) and n vinyl pyrolidone (NVP) mono-mers, both of which absorb high amounts of water and are usually adjuncts to HEMA to increase lens water content
Ethylene glycol dimethacrylate (EGDMA), a cross-linking agent that adds dimensional stability and stiffness but reduces water content

20. Copolymers 38 percent (low-water content) HEMA monomer + NVP or MAA
Increase water content to medium (about 50 percent) or even high (about 70 percent)
+ MMA and/or EGDMA
increases material durability, elasticity and stability but decreases water content.

21. Homogenous Soft Hydrogel Contact lenses
Poly(vinyl alcohol)
CIBA:daily disposable lens.
Omafilcon A, Proclear, Biocompatibles Inc.
59% hydration
better water retention than other conventional hydrogel lenses
The original
hydrogel contact lens material was poly(2-hydroxyethyl
methacrylate) (PHEMA) (Wichterle and Lim, 1960); at equilibrium
swelling in physiological saline solution it contains
about 40% water of hydration. (Hydration of hydrogel contact
lenses is customarily given as a percentage of water by weight,
on a wet basis.)
The soft hydrogel contact lenses (SCL) are supple and
fit snugly on the corneal surface. Because there is little tear
exchange under these lenses, most of the oxygen that reaches
the cornea must permeate through the lens. The oxygen permeability
coefficient of the standard hydrogel materials increases

22. Additives polymer chains to move more freely within the material
may serve to block the transmission of ultraviolet light
may help the material resist dehydration.

23. Anything dissolved in the water has the potential to enter into the polymer depending on its molecular size and the pore size in the material.
The pore size of low-water content lenses is about 0.5μm and may be as high as 3.5μm with high-water lenses.

24. SOFT HYDROGEL CONTACT LENSES FDA classifications
Homogeneous hydrogels
Heterogeneous hydrogels
Hydrophobic siloxane-hydrogel
High oxygen permeability
less likely to adsorb proteins
Low water <50% non-ionic
High water > 50% non-ionic
Low water ionic
High water ionic
more likely to absorb lipids
May absorb much higher amounts of protein
prone to be sensitive to pH changes interact with some solutions

25. IONIC : methacrylic acid
Hydration but,
Protein binding
HIGH WATER CONTENT
Oxygen permeability
Friability (fragile)
Protein penetration
Dehydrate faster (temp changes and water evaporation)
Physiologically and optically best daily wear lens is ultrathin low-water content contact lens
But thinner it is faster it dehydrates
induce corneal epithelium injuries by a mechanism still unclear.

26. DAILY WEAR:
open eye
standard hydrogel contact lenses
DAY AND NIGHT:
Up to 1wk
higher oxygen transmissibility

27. HETEREOGOUS SOFT GEL CONTACT LENSES

28. 1. Siloxane-hydrogel Contact Lenses
Goal:
Comfort of a hydrogel
Increased oxygen permeability
Continues use of 1 month
Solution:
Copolymers of hydrophilic monomers with end functionalized siloxanes
Siloxanes such as PDMS (silicone) or TRIS
End product:
Oxygen permeability mainly through siloxane
Siloxane is on the surface
RF-plasma reactor to make the surface hydrophilic
Cause unstable surfaces-no long term advantage

29. Variation of oxygen permeability (Dk) with equilibrium
water content for conventional and silicone-containing
hydrogels. (Adapted from Silicone hydrogels -- the rebirth of
continuous wear, Butterworth Heinneman, 2000)

31. Examples Purvision Balafilcon from Bausch & Lomb (36% water)
O2 permeability : 110 × 10−11 cm2 (STP) cm2/(cm3 sec mm Hg)
Dk of balafilcon A is 99
TRIS derivative + NVP :polar, hydrophilic
First generation

32. PureVision surface treatment by plasma oxidation technique
Forms hydrophilic glassy islands of inorganic silicate with exposed hydrophobic balafilcon material in between
The gaps between the islands are so small that the wetting of the glassy silicate completely covers over the small hydrophobic interspaces, changing the surface chemistry from a hydrophobic silicone to hydrophilic silicate.
The flexibility of the lens material does not adversely affect the
surface integrity or the wettability of the lens surface.
FDA Group III (low water, ionic).
Atomic force microscopy
(contrast mode 50 x 50μm) image
of unused PureVision lens.

33. Focus Day&Night Lotrafilcon from Ciba
(24% water)
O2 permeability : 175 × 10−11.,
Dk of lotrafilcon A's is 140
Plasma treatment
ultrathin (25nm) hydrophilic layer on the lens surface, hiding the TRIS structures underneath
Biphasic with small domain size for optical transperency
Fluoroether/silicone macromer + TRIS monomer + hydrophilic monomer DMA (N, N-dimethylacrylamide).
fluorosiloxane phase allows for high oxygen permeability
hydrogel phase transmits ions and water, allowing adequate lens moveme
First generation

35. 1st generation
higer water content lower Dk
Typical for silicone/siloxane

36. 2nd generation
more hydrophilic
long-chain, high-molecular-weight polyvinyl pyrrolidone (PVP)
Internal wetting agent
lower modulus

37. 3rd generation
different chemistry, different trend
long-chain siloxane macromer
high oxygen permeability + high water + relatively low modulus
inherently wettable

38. Second-Generation Silicone Hydrogels
Galyfilcon A and senofilcon A
more hydrophilic derivative of the TRIS monomer
+ siloxy macromer
+ hydrophilic monomers such as HEMA and DMA.
no surface treatment is applied
incorporate a long-chain, high-molecular-weight polyvinyl pyrrolidone (PVP)
internal wetting agent
hydrophilic humectant, meaning that it attracts and retains moisture with the intent of keeping the lenses hydrated throughout the wearing day.

39. Second-Generation Silicone Hydrogels
Galyfilcon A and senofilcon A
Lower modulus
Mechanical issues related to higher modulus ones:
epithelial arcuate lesions, mucin balls, contact lens papillary conjunctivitis, conjunctival epithelial flaps

40. Third-Generation Silicone Hydrogels
Comfilcon A (Biofinity, CooperVision)
Enfilcon A (Avaira, CooperVision)
long-chain siloxane macromer
high oxygen permeability
relatively low modulus
inherently wettable — no internal wetting agent or surface treatment is required
have a fundamentally different chemistry

41. 2. Flexible perfluoropolyether lenses
OXYGEN PERMEABILITY
LOW BACTERIAL ADHESION
Copolymer with MMA (for rigidity) and VP (for wettability)
flexible, nonhydrated

42. Proclear