1

Clinical Considerations with Silicone Hydrogel Lenses

Maurice J Wilson, OD

Agenda

The science behind the lensesOxygenSurfaceDesignLens care and silicone hydrogel lensesComfort & adaptation issues

The Science Behind the Lenses

HEMA-based materials– Positives

Easily fabricated into CL’sRelatively cheap to produceHighly flexibleDimensionally stable to changes in pH & temp.

– NegativesReliance on H2O to transport O2

– Limitation to amount of O2 transmitted to cornea– Corneal oxygen deficiency

O2 transport – HEMA materials

27

55

28

55

32

66

26

58

0

20

40

60

80

100

120

140

160

180

Dk/t H20

Dk/t and H2O

Frequen

cy®

55.

Biomedics

®

Soflens®

66

ACUVUE® 2

Primary means of ↑ Dk/t is to ↑ H2O

H2O has limited ability to dissolve & transport O2

Dk of H2O approx. 80– “100% H2O lens” Dk = 80

Corneal Oxygen DeficiencyClinical signs

- Conjunctival injection - Limbal redness

- Neovascularization - Corneal staining

- Refractive error shift - Corneal neovacularization (myopic shift of ≥ 0.50 D)

- Corneal edema - Corneal distortion

- Increased bacterial binding - Endothelial polymegethism, pleomorphism & ↓ cell density

- Keratometry/topographical - Increased corneal changes and distortion thickness

2

Corneal Oxygen Deficiency

Patient symptoms

- End-of-day discomfort, itching - Reduced wearing time or dryness

- Lens awareness - During day / end-of-day dryness

- Sore, irritated eyes - End-of-day burning

- Blurred, reduced, or - Photosensitivity fluctuating vision

- Scratchy, uncomfortable - Transient halo around lights feeling

- Spectacle blur

Dk of silicone?

Approx. 400

The Science Behind the Lenses

Silicone-based materials– Positives

Exceptional O2 transmissibilityDurability

– NegativesPoor fluid transport

– Lens binding – Surfaces extremely hydrophobic

Increased modulusLipid deposition

The Science Behind the Lenses

Silicone hydrogel materials – Silicone rubber combined with conventional

hydrogel monomersSilicone component provides extremely high O2 permeabilityHydrogel component facilitates flexibility, wettability and fluid transport

– Like combining oil & water – Over 20 years to be successfully created!

The science behind silicone hydrogel lenses

Dumbleton, Oct. 2002 The Physical and Clinical Characteristics of Silicone Hydrogel Lenses: How They Work? www.siliconehydrogels.org 2005-1-0005

3

27

55

28

55

32

66

26

58

86

47

101

36

138

33

147

38

175

24

020406080

100120140160180

Dk/t H20

Dk/t and H2O

Conventional Lenses Silicone Hydrogels

ACUVUE®

OASYS™

PureV

ision

®

NIGHT &

DAY

®

Frequen

cy®

55.

Biomedics

®

Soflens®

66

ACUVUE® 2

O 2OPTIX

™

ACUVUE®

Advance

™

18.9%20.0%

25.3%

26.8%

22.0%23.4%

17.6%16.7%

15.5%15.2%14.4%14.0%14.4%

13.8%12.8%11.4%

9.2%

7.5%

5%

10%

15%

20%

25%

30%

Jan04

Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec Jan05

Feb Mar Apr May Jun

Source: A.C. Nielsen, excludes WalMart, mail order/Internet

Silicone Hydrogel Lens Market Share

(% of U.S. retail sales)

Silicone Hydrogel Market Share Forecast

25%

34%

44%

68%61%53%

47%

32%39%

56%

66%75%

2005 2006 2007 2008 2009 2010

Hema Lenses

Silicone Hydrogels100%

Source: CIBA Vision forecast

(% of U.S. retail sales)

Silicone Hydrogel Lens Materials

mPDMS + DMA + EGDMA + HEMA +siloxane macromer + PVP

mPDMS + DMA + HEMA + siloxane macromer + TEGDMA + PVP

NVP + TPVC + NCVE + PBVC

DMA + TRIS + siloxane macromer

DMA + TRIS + siloxane macromer

Principal monomers

IIIIIIIFDA group

No surface treatment.Internal wetting agent (PVP) throughout the matrix that also coats the surface

No surface treatment. Internal wetting agent (PVP) throughout the matrix that also coats the surface

Plasma oxidation process

25 nm plasma coating with high refractive index

25 nm plasma coating with high refractive index

Surface treatment

86147101138175Oxygen transmissibility (× 10–9)

6010391110140Oxygen permeability (× 10–11)

2 weeks1-2 weeks4 weeks2 weeks4 weeksRecommended replacement schedule

+ 8.00 to –12.00-0.50 to –6.00+6.00 to –12.00+6.00 to -10.00+6.00 to –10.00Prescription range (D)

8.3; 8.78.48.68.68.4; 8.6Back optic zone radius

14.014.014.014.213.8Total diameter

47%38%36%33%24%Water content

0.070.070.090.080.08Center thickness (@ –3.00 D) mm

VistakonVistakonBausch & LombCIBA VisionCIBA VisionManufacturer

galyfilcon Asenofilcon Abalafilcon Alotrafilcon Blotrafilcon AUnited States adopted name

Acuvue AdvanceAcuvue OASYSPureVisionO2OPTIXFocus Night & DayProprietary name

Oxygen :How Much Is Enough?

2005-1-0005

Oxygen: How Much Is Enough?Overnight wear– Holden & Mertz3 (1984)

Assuming 4.0% edema, min. Dk/t = 87 for EW

– Sweeney4 (2003)Assuming 3.2% edema, min. Dk/t = 125 for EW

– Harvitt & Bonanno5 (1998) No stromal anoxia, min. Dk/t = 125 for EW

Daily wear– Holden & Mertz3 (1984) =24– Harvitt & Bonanno5 (1998) = 35

3. Holden BA. Mertz G. Critical oxygen levels to avoid corneal edema for daily wear and extended wear contact lenses. Invest Ophthalmol Vis Sci 1984;25:1161-7.

4. Sweeney DF. Clinical signs of hypoxia with high Dk soft lens extended wear: Is the cornea convinced? Eye & Contact Lens 2003;29(1S) S22-S25.

5. Harvitt DM. Bonanno JA. Re-Evaluation of the Oxygen Diffusion Model for Predicting Minimum Contact Lens Dk/t Values Needed to Avoid Corneal Anoxia. Optometry and Vision Science 1999;6:712-9.

4

There Is Some Consensus

To achieve corneal swelling equivalent to no lens in EW2

To avoid corneal anoxia in overnight wear3

To avoid an increase in limbal hyperaemia in daily wearor extended wear4

– Implications for limbal stem cells which are critical for the long term growth and repair

To reduce bacterial binding for daily wear or extended wear5

3 Silicone Hydrogels, ed. Sweeney, page 93 (2000)4 Harvitt and Bonanno (1999): Re-evaluation of the oxygen diffusion model for predicting minimum contact lens Dk/t values to avoid corneal anoxia.5 Papas, E. On the relationship between soft contact lens oxygen transmissibility and induced limbal hyperemia. Exp Eye Res 1998;67(2):125-131.6 Cavanagh in Ghormley (2005): How Much Oxygen is Enough for Safe Lens Wear (CL Spectrum - March)

A minimum Dk/t is required:

Important Factors to Consider

These studies all represent the AVERAGE response– Average represents 50% of your patients

Patients exhibit widely different corneal swelling responses6

Corneal oxygen demand increases with age7

50% Pass 50% Fail

Dk, Dk/t and “Local Oxygen Transmissibility”

2005-1-0005

O2

O2

O2

O2

O2

Dk

Dk, Dk/t and “Local Oxygen Transmissibility”

2005-1-0005

O2

O2

O2

O2

O2

Dk Dk/t =

O2

O2

O2

O2

O2

?

?

?

?

?

thickness = “t” “t”

↑t → ↓Dk/t

material Dk divided by the local thickness (cm.)

Given two silicone hydrogel lenses, can one with a lower Dk have a

higher Dk/t than the other?

103ACUVUE OASYS

110O2OPTIX

DkLens

Given two silicone hydrogel lenses, can one with a lower Dk have a

higher Dk/t than the other?

103ACUVUE OASYS

110O2OPTIX

DkLens Dk/t

138

147

Center Thickness

(-3.00)

0.08

0.07

5

Oxygen Transmissibility Profile

-3.00 Model

0

20406080

100120

140160180200

Dk/

t

Edge

Periph

ery

Mid-peri

ph

Optica

l zon

e

Center

thick

ness

Optica

l zon

e

Mid-peri

phery

Periph

ery

Edge

Acuvue 2 Advance O2Optix NIGHT & DAY

175

138

86

26

NIGHT & DAY

O2 OPTIX

AV Advance

AV 2

Oxygen Profiles (-3.00 sph.)

Ordinary hydrogel lens N&D contact lens

Bulbar Redness

Limbal Redness

Vascularization

•Limbal hyperemia is directly related to soft contact lens oxygentransmissibility in the peripheral (local) area of the lens.6

Localized Oxygen Transmissibility at Lens Periphery

6. Papas E. On the relationship between soft contact lens oxygen transmissibility and induced limbal hyperaemia. Exp Eye Res 1998;67:125-31. 2005-1-0005

•The minimum Dk/t necessary to avoid limbal hyperaemia in daily wear = 125.6

Variables…

1. There is a high variability in oxygen metabolism and no simple test to predict oxygen requirements for a given individual lens wearer

2. Actual oxygen transmissibility (Dk/t) varies across a given lens profile and is significantly impacted by lens power

AND…

Variability in Lifestyle & Compliance

36% 30-Day

Continuous Wear

28% Daily Wear

36%Occasional

Overnight to 2-Week

Continuous Wear

% of patients preferring each wear regimen

CIBA Vision, data on file 2004

72% desire some form of overnight wear!

6

28% of 1- 2 week lens wearers occasionally or routinely sleep in their lenses(Source: CIBA Vision, data on file, 2003)

84% of soft contact lens wearers have napped with lenses (Source: CIBA Vision, data on file, 2004)

They’re already doing it!

Oxygen :How Much Is Enough?

2005-1-0005

Oxygen:How Much Is Enough?

2005-1-0005

O2: How Much Is Enough?

Holden & Mertz3 (1984) – Assuming 4.0% edema, min. Dk/t = 87 for EW

Sweeney4 (2003)– Assuming 3.2% edema, min. Dk/t = 125 for EW

Harvitt & Bonanno5 (1998) – No stromal anoxia, min. Dk/t = 125 for EW

3. Holden BA. Mertz G. Critical oxygen levels to avoid corneal edema for daily wear and extended wear contact lenses. Invest Ophthalmol Vis Sci 1984;25:1161-7.

4. Sweeney DF. Clinical signs of hypoxia with high Dk soft lens extended wear: Is the cornea convinced? Eye & Contact Lens 2003;29(1S) S22-S25.

5. Harvitt DM. Bonanno JA. Re-Evaluation of the Oxygen Diffusion Model for Predicting Minimum Contact Lens Dk/t Values Needed to Avoid Corneal Anoxia. Optometry and Vision Science 1999;6:712-9. 2005-1-0005

Clinical Research = Populations

Clinical Care = Individuals

Shouldn’t we choose Dk/t with theleast physiologically tolerant

patient in mind?

2005-1-0005

Surface Modifications

7

Lens Surface Modifications

Silicone elastomer materials generally display:– Decreased surface wettability– Increased lipid interaction– Accentuated lens binding

Require “surface modification”

Surface Modifications

O2OPTIX NIGHT & DAY

PureVisionACUVUE Advance ACUVUE OASYS

Permanent, chemically bonded plasma treatment

for a smooth, continuous surface

Surface coating made up of silicate islands that do not

completely cover the surfaceNo permanent

plasma treatment

Modulus

Modulus

Definition: Force per unit area required to produce a deformation– Describes how well a material resists deformation

Modulus is a material parameter– Effective stiffness of a particular contact lens will also be influenced by

its specific geometry – A lens with a low modulus may still be relatively stiff if it has a thick and

chunky design

0.43ACUVUE Advance0.72ACUVUE OASYS1.0O2OPTIX1.1PureVision1.5NIGHT&DAY

Modulus (MPa)Name

↑ modulus– Improved handling– Less “draping” over cornea

Fitting implications– Possible masking of astigmatism

Modulus

↑ modulus: Possible physiological effects– Mucin balls– Superior epithelial arcuate lesions (SEAL)– Contact Lens Induced Papillary Conjunctivitis

(CLPC)

Modulus

8

Mucin Balls

Pearly, translucent, post-lens debris

– mucin & lipid – common after EW of Si-H– 20-100 µm– tear film collapses, lipid

contacts mucin, rolls up following lens / eye movement

Mucin Balls

No effect on symptoms, vision or biomicroscopy

Not related to age, gender or prescription

Higher incidence found if:– steep cornea

– 30 day EW vs. 6 day EW

– no use of rewetting drops

Mucin Balls

No complications over short term

If severe:– reduce nights without removal

– move the lens onto the sclera periodically

– use rewetting drops am and pm

– fit steeper lens, i.e., 8.4mm base curve

Superior Epithelial Arcuate Lesions

(SEALs)

Superior Epithelial Arcuate Lesions (SEALs)

• Thin arcuate lesion superior cornea ~ 1mm from limbus

• Significant staining

• Occasionally underlying infiltrates

• Edges often irregular

SEAL (Epithelial Splitting)Mechanical forces from upper lid are transmitted to superior cornea resulting in epithelial chafing.

May be related to– Improperly fit high modulus,

stiff materials– Wearing schedule (EW)– Thick designs– Poorly blended curve junctions– Low water content?– Tight upper eye lids– Certain corneal topographies

9

SEAL (Epithelial Splitting)

Symptoms– Pt’s often

asymptomatic!– Most common

symptomsFBSIrritation

Contact Lens Papillary Conjunctivitis

(CLPC)

Contact Lens Papillary Conjunctivitis (CLPC)

General CLPC• Large, raised papillae of a

cobblestone appearance• Moderate to severe hyperaemia

across the entire tarsus • Moderate to severe patient

symptoms, including itching or irritation, a stringy or ropy discharge, excessive movement of the lens and blurred vision due to this movement or coatings/discharge on lenses.

Local CLPC• Involves papillae and hyperaemia

confined to one or two areas of the upper tarsus only, usually in the central region nearest the lid margin

• Symptoms typically much milder than in general CLPC, with slight irritation or foreign body sensation often the only symptom.

Contact Lens Papillary Conjunctivitis (CLPC)

Higher modulus?– SiHy: ↑ incidence of “local” CLPC

(≤ 2 zones involved)– Low Dk/t: ↑ incidence of “general” CLPC

(› 2 zones involved)– N&D: Lower incidence 8.4 BC vs. 8.6 BC

High recurrence rate if refit same SiHy material and continue EW

Recurrence rate significantly reduced with DW of same SiHy material

Optics Optics

NIGHT&DAY and O2OPTIX– Advanced aspheric lenses designed to

optimize visual clarity PureVision – Aspheric optical design to correct spherical

aberrationACUVUE Advance and OASYS– No asphericity

10

Optics

Two factors may influence lens power in fitting / refitting silicone hydrogel lenses

1. Variations in optical designs require careful over- refraction in refitting

2. Reversal of myopic creep

Spherical Aberration5 mm “Optic Zone”

POWER PROFILECenter 2.5 mm

RX +6.00

RADIUS (mm)

RX

(Dio

pter

s)

4

5

6

7

8

9

0.0 0.5 1.0 1.5 2.0 2.5 3.0

PRODUCT: Acuvue2

PRODUCT: FN&D8.6

RX +6.00

RADIUS (mm)

RX

(Dio

pter

s)

4

5

6

7

8

9

0.0 0.5 1.0 1.5 2.0 2.5 3.0

PRODUCT: Acuvue2

PRODUCT: FN&D8.6

Spherical Aberration5 mm “Optic Zone”

-4-3

-2-1

012

3

Pow

er d

iffer

ence

Cent

er to

2.5

mm

-9.00 -6.00 -3.00 +3.00 +6.00Labelled Power

etafilcon A lotrafilcon A

-4-3

-2-1

012

3

Pow

er d

iffer

ence

Cent

er to

2.5

mm

-9.00 -6.00 -3.00 +3.00 +6.00Labelled Power

etafilcon A lotrafilcon A

Effect of Reduced Aberration

Plus Acuvue 2 lenses “act” more plus– Patient wearing +5.00 AV2– Switch to NIGHT & DAY, +5.50 needed?

Minus Acuvue 2 lenses “act” more minus– Patient wearing -7.00 AV2– Switch to NIGHT & DAY, -7.50 needed?

Examples:

“Myopic Creep”

-1

-0.5

0

0.5

0 3 6 9

Mea

n C

hang

e in

Sph

eric

al R

efra

ctio

n (D

)

Time (months)

etafilcon A

lotrafilcon Ap = NS

p = 0.006

Reversal of myopic creepetafilcon A to lotrafilcon A - 3 month cross over: n=13

-4

-3.5

-3

-2.5

B1 3 6 9 B2 3

Mea

n Sp

heric

al R

efra

ctio

n (D

)

Time (months)

etafilcon A EWp=0.004

etafilcon A DWp=NS

lotrafilcon A EWp=0.003

//

11

Lens Care&

Silicone Hydrogel Lenses

Modern Lens Care Convenience

Current one- step, no- rub, multipurpose (MPS) systems generally contain one of three antimicrobial agents:– Hydrogen peroxide– Polyhexamethylene biguanide (PHMB)– Polyquaternium-1 (Polyquad)

2005-1-0005

Introduction of Silicone Hydrogels

Anecdotal reports of corneal staining

Question of interaction between certain lenses and lens care products?

2005-1-0005

Summary

0%1721%14

24%178%150%14,15N&D

N/A37%16

47%142%160%14PureVision

AQuifyMPS

ReNuMultiplus

Polyquad-based

PHMB-basedPeroxide-based

Jones, 2004.2005-1-0005

Summary

• Unacceptable staining is more likely when PureVision lenses are used with certain PHMB-based systems than when N&D lenses are used with the identical systems

• Staining is relatively rare with Polyquad-based regimens, and essentially non-existent with hydrogen peroxide-based systems

• Regimens with identical concentrations of PHMB can behave differently, depending on solution formulation

Jones, 2004.

2005-1-0005

Summary

Success of a given lens care regimen with conventional hydrogel lenses does not guarantee success of that same system with silicone hydrogel lenses (emphasis added)

When refitting DW patients from conventional hydrogel lenses to silicone hydrogel lenses, we tend to blame discomfort on the new lens material (emphasis added)

Must consider potential interaction between material and care regimen

Jones, 2004.

2005-1-0005

12

“ The ultimate key to success with these novel contact lens materials is to make specific lens care recommendations to every patient …”

- Dr. Jennifer Smythe

Smythe J. A New Generation of Contact Lens Care. Optometric Management March, 2005.

Comfort &

Adaptation

Comfort?

Silicone hydrogel lenses are stiffer than conventional HEMA-based materialsMany patients will experience increased “awareness” when refit

Educate & Set Proper Expectations

Discuss up front!Awareness may increase before it gets better (PMMA RGP)

So how do I decide?

The “Pepsi Challenge”

vs.

13

The “Pepsi Challenge”

vs.

What’s going on?

Comfort and wettability

“Of the silicone hydrogel lenses used, balafilcon A (PureVision®) had the highest

contact angles; galyfilcon A (Acuvue®

Advance™) was the most wettable initially but rapidly developed contact angles similar to balafilcon A (Pure Vision); and lotrafilcon

materials (NIGHT & DAY® and O2OPTIX™) retained the most wettable surface overall.”1

1. Rogers R, Jones L. In vitro and ex vivo Wettability of Phema and Siloxane-Based Contact Lens Polymers. Invest Ophthalmol Vis Sci 2005;46; E-Abstract 918.

End of day comfort and dryness

Dumbleton2 (2004)– Group of successful long- term soft contact lens

wearers were refitted with silicone hydrogel lenses (CIBA Vision Night & Day™ )

DW basis and replaced monthly

2. Dumbleton KA, Keir N, Moezzi A, Jones L, Fonn D. Redness, dryness and comfort following refitting long term low Dk hydrogel wearers

with silicone hydrogels. Optom.Vis.Sci. 2004;81:31.

Dumbleton2 (2004)

– Results:Significantly better end-of-day comfort and less end of day dryness when compared with their habitual lensesWhile end-of-day comfort remained the same throughout the study, there was actually less end of day dryness as the study progressed The intensity of dryness symptoms at the end of the first month and throughout the second month was significantly lower than after the first day and first week wearing the silicone hydrogel lenses

End of day comfort and dryness

2. Dumbleton K. Daily wear performance of Silicone Hydrogel Lenses. www.siliconehydrogels.org June, 2005.

Limbal Hyperemia•“…showed a significant decrease in limbal hyperemia within one month of refitting conventional hydrogel lens.” 2 (emphasis added)

“Bulbar and limbal hyperemia decreased significantly during the study. The reduction … occurred mainly between the baseline and 1 month visits.3

(emphasis added)

2. Dumbleton K. Daily wear performance of Silicone Hydrogel Lenses. www.siliconehydrogels.org June, 2005. 3. Dumbleton et al. Redness, dryness and comfort following refitting long term low Dk hydrogel lens wearers with silicone hydrogel lenses. Optometry and Vision Science 81 (12S):31.

So how do I decide?

“Does this mean that the Pepsi Challenge was a fraud? Not at all. It just means that we have one reaction after taking a sip, and we have another reaction after drinking a whole can. In order to make sense of people’s cola judgments, we need to first decide which of those two reactions most interests us.” (emphasis added)

- Malcolm Gladwell As quoted in “blink”

14

“Most people have a desire to look for the exception instead of the desire to become exceptional.”

- John Maxwell

2005-1-0005

Questions &

Discussion

2005-1-0005

Thank you!

2005-1-0005