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SOFT LENS MATERIAL FITTING & FOLLOW-UP EVALUATION
University of Missouri-St. Louis College of Optometry
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Advantages Initial comfort Little lag Simple to fit Inventory
Quick adaptation Occasional wear Hard to dislodge Difficult to get trapped FB Rarely causes tearing Cosmesis
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Disadvantages Bacterial contamination/greater risks with noncompliance
Care? Durability Prone to deposits Reduced oxygen permeability with hydrogel materials Quality of vision Difficult to verify Limitations of correction
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Materials Chemical monomers linked to form chains of polymers, cross-linked loosely polyHema Add other monomers to improve HEMA MAA, MMA, GMA, PVA Silicone Hydrogels
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Monomer Characteristics
HEMA – hydrophilic, soft, wettable, low Dk EGDMA – Stable, low Dk MAA – hydrophilic, pH sensitive MMA – Hard, no Dk, machinable, optical clarity, stable NVP – Hydrophilic, wettable, high water uptake, High Dk, pH sensitive
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Monomer Characteristics
GMA – Wettable, deposit resistant, low Dk PVA – Hydrophilic, high water uptake, Deposit resistant Silicone – hydrophobic, High Dk
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The Science Behind the Lenses
HEMA-based materials Positives Easily fabricated into CL’s Relatively cheap to produce Highly flexible Dimensionally stable to changes in pH & temp. Negatives Reliance on H2O to transport O2 Limitation to amount of O2 transmitted to cornea Corneal oxygen deficiency For the most part, HEMA is an excellent material from which to make soft contact lenses. The one huge negative, however, is the reliance on water to transmit oxygen through the lens material to the cornea. This factor, which significantly limits the amount of oxygen available to the cornea, may over time lead to chronic corneal hypoxia and an array of signs and symptoms known collectively as “corneal oxygen deficiency”. This will be discussed in greater detail in a moment, but first let’s examine the limitations brought about by HEMA’s dependence on water to transmit oxygen.
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O2 transport – HEMA materials
This illustration is used to simulate the movement of oxygen molecules through the contact lens to the underlying cornea. With conventional HEMA –based materials, oxygen molecules are transmitted through the material by means of the water portion of the polymer.
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Silicone Hydrogels Available
Focus Night & Day O2 Optix & Air Optix Aqua AV Advance AV Oasys PureVision Biofinity Material Lotrafilcon A Lotrafilcon B Galyfilcon A Senofilcon A Balafilcon A Comfilcon A Dk 140 110 60 103 101 128 Dk/t 175 138 86 147 160 Water content 24% 33% 47% 38% 36% 48% Powers +6 to -10 +8 to -12 +6 to -12 -0.25to -10 BCR 8.4, 8.6 8.6 8.3, 8.7 8.4, 8.8 8.3, 8.6 Replace Monthly 2-4 weeks 2 weeks
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Silicone Hydrogels Available
Avaira O2 Optix Custom Premi O Material Enfilcon A Sifilcon A AsmofilconA Dk 100 82 129 Dk/t 125 117 161 Water content 46% 32% 40% Powers -0.25 to -6 +20 to -20 BCR 8.5 7.4 to 9.2 Replace 2 weeks 3 months
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Other Dk/t Values Soflens 38 = 21 AV2 = 20 Focus Monthly = 15
Focus Dailies = 27 SF 1 Day = 16 Proclear = 30
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Pure Vision (B&L) Performa surfacing process
Do not use abrasive cleaners, H2O2, Miraflow Glassy islands Available in toric & multifocal DW/EW/CW
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Focus Night & Day, Air Optix Aqua O2 Optix & O2 Optix Custom (Ciba)
No restrictions on care solutions Plasma coating Surface chemically uniform Uniformly coated with hydrophilic polymer N&D DW/EW/CW, Air & O2Optix DW/EW, O2 Optix DW, Air Optix for Astigmatism
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Acuvue Advance & Oasys (Vistakon)
AV2 design, UV blocker No coating, Hydraclear wetting agent on surface and throughout lens AV Adv. DW, Oasys DW/EW Toric and Multifocal
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Biofinity & Avaira (CooperVision)
Company reports no surface treatment or wetting agents Aquaform comfort science DW at this time
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Lens Surface Modifications
Silicone elastomer materials generally display: Decreased surface wettability Increased lipid interaction Accentuated lens binding Require “surface modification” Another important aspect of silicone hydrogel technology is the surface treatment of the lenses. One of the challenges historically to the development of silicone hydrogel lenses is the fact that silicone, by nature, is a very dry, hydrophobic material, and exposed silicone surface at the surface of a contact lens will lead to decreased wettability, increased lipid interaction and accentuated lens binding. In order to render the surfaces hydrophilic, the surface of all silicone hydrogel lens must be “modified” in some manner.
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Surface Modifications
All photos 5 x 5 micron resolution Permanent, chemically bonded plasma treatment for a smooth, continuous surface O2OPTIX NIGHT & DAY Each company has developed its own means of accomplishing this, but the techniques, and therefore the surface characteristics of the various lenses, vary significantly. The differences in the surfaces can be visually appreciated using very high magnification imaging techniques such as atomic force microscopy (AFM), as shown in these photos. CIBA Vision utilizes a unique, patented process called “plasma polymerization” which results in a permanent, chemically bonded plasma treatment for a smooth, continuous surface. B&L also utilizes a plasma treatment for its PureVision lenses, but this process, called “plasma polymerization” differs from the CIBA Vision process in that the silicone components on the surface of the lenses are transformed into hydrophilic silicate compounds surface, forming glassy, island-like, discontinuous silicate “islands which do not completely cover the surface. The ACUVUE Advance and ACUVUE OASYS materials have no permanent plasma treatment, relying instead on an internal wetting agent (Hydraclear™) which is designed to provide a hydrophilic layer at the surface of the material. (Source: Jones L and Tighe B. Silicone Hydrogel Contact Lens Material Update – Part 2, editorial, 2004(August).) PureVision ACUVUE Advance ACUVUE OASYS Surface made up of silicate islands that do not completely cover the surface No permanent plasma treatment
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Surface Modifications
Focus N&D, O2 Optix, Air Optix O2 Optix Custom PureVision AV Advance, AV Oasys Biofinity, Avaira PremiO Ciba Vision Bausch & Lomb Vistakon CooperVision Menicon Plasma coating Plasma oxidation Internal Wetting agent- polyvinyl pyrrolidone (PVP) None Nanogloss Ciba Vision -gas plasma technique to apply a uniform plasma coating, approximately 25 nm thick with high refractive index. The gas plasma technique is also used by Bausch and Lomb to apply a plasma oxidation surface treatment. PremiO reports similar surface modification.
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Biofinity Siloxane molecules attract and bond to surrounding water molecules, continuously wetting and lubricating the material (Courtesy CooperVision)
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Modulus “Stiffness” Makes it easier to handle Masks astigmatism?
Modulus impacts the “stiffness” of a lens material, and is defined as… The comparative modulus measurements of the currently available silicone hydrogel lenses are listed here. However, it is important to note that, like Dk, modulus describes only a material parameter, and is therefore also related to thickness. A thin lens of relatively high modulus could be less “stiff” than a thick lens of lower modulus.
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Increased Modulus Mucin Balls GPC/CLPC SEALs Edge Fluting
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Modulus Material Hydrogel/SiHy Modulus (MPa) HEMA Hydrogel 0.50
AV Advance SiHy Avaira 0.5 AV Oasys Biofinity PremiO 0.9 O2Optix/Air Optix 1-1.2 PureVision Focus N&D
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An increased Dk is linked with an increase in modulus
SiH Dk & MODULUS An increased Dk is linked with an increase in modulus Night&Day O2Optix Purevision Modulus (MPa) biofinity Oasys Advance Dk Courtesy CooperVision
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Comfort? Silicone hydrogel lens materials are different from conventional HEMA-based materials Some patients will experience increased “awareness” when refit There has been a considerable amount of discussion regarding “comfort” when refitting patients from low-Dk/t lenses to silicone hydrogels. It is important to note that, as a category, silicone hydrogel lenses are “stiffer” than conventional HEMA-based materials, and therefore some patients may indeed report an increased awareness of the lenses for a time following refitting. (This is not typically a factor with new fits as the patient has no reference point from which to make a comparison.)
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Dailies with AquaRelease (Ciba) AV 1Day Moist (Vistakon)
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Water content = weight of water in lens/ total lens weight X 100
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Water Content Range of water content 24-79%
HEMA by itself has 38% water Plays a role in determining: Dk/t, durability, stability, deposit formation, pore size
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Silicone Hydrogels Hema – Hydrophilic Silicone – Hydrophobic
Dk-Hema = 10 Dk-Silicone = 250
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Dk compared with % Water
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Dk/t and H2O Conventional Lenses Silicone Hydrogels
These relationships are beautifully illustrated in this graph. As can be seen, increasing water content of conventional lenses does slightly increase the resultant Dk/t, but still to a very low level. With the silicone hydrogel lenses shown, Dk/t levels climb significantly with increased silicone content of the lenses and generally decreasing water content. (One may also wonder how the Acuvue OASYS can have a higher water content than O2OPTIX and PureVision, yet still have a higher Dk/t. That has to do with the different center thicknesses of the lenses, and will be discussed further in a later portion of this presentation.) ACUVUE® OASYS™ NIGHT & DAY® Biomedics® Soflens®66 ACUVUE®2 ACUVUE® Advance™ PureVision® O2OPTIX™ Frequency® 55. Conventional Lenses Silicone Hydrogels
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FDA Classification Group 1 – nonionic, low water
Group 2 – nonionic, high water Group 3 – ionic, low water Group 4 – ionic, high water Group 5 - ???????
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Groups 2 & 4 avoid Heat disinfection Sorbic acid/potassium sorbate
Deposit-prone patient
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Oxygen Permeability Increases with water content in HEMA lenses
Increases as water content decreases in Silicone Hydrogels Oxygen transmission increases with decreases in CT Dk ranges 8.3 to >100 Tear exchange 1-2%
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Oxygen Profiles (-3.00 sph.)
Another way to illustrate this concept is by using color to represent the oxygen profile across the lens profile. Again, depending on the thickness profile of a given lens, lenses of seemingly similar “published Dk/t”, (at the center of a sph. lens), can have significantly different oxygen transmissibility profiles throughout the mid-peripheral and peripheral regions of the lens. Two important points to note: The cornea does not have the ability to move oxygen laterally or peripherally. Therefore, the amount of oxygen moving through a lens at a given point is what is available to the corneal tissues directly beneath. The limbal region is of particular interest due to the fact that it is the only source of stem cells in the eye, leading some experts to speculate on the long-term implications of contact lens-related hypoxia. (Barr JT, Fonn D, Bonanno JA, Cavanagh HD, et al. Elemental Need: Sustaining Limbal Health, Contact lens Spectrum Supplement, August 2005; p. 11.)
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Examples Hydrocurve II 45%, Dk 12, CT .05, Dk/t 24
Optima 38, Dk 8.5, CT .06, Dk/t 14 Optima FW, Dk 8.5, CT .035, Dk/t 24 B&L 70, Dk 33.8, CT .1, Dk/t 33.8
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Wettability Aids in lid closure and comfort
Contaminants adhere to surface Increase sensitivity to preservatives
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Internal Wetting Agents
Polyvinyl pyrrolidone (PVP) Polyvinyl alcohol (PVA)
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Material Selection Patients with Ocular Compromise
Refractive Error including astigmatism Deposit-prone patients Age Lens Handling Part-time Wearers Compliance Oxygen requirements Patient’s Interest Dry Eye
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Soft Lenses for Dry Eye Proclear Extreme H2O AV Advance Preference CSI
Dailies with Aquarelease AV 1 day Moist O2 Optix/Air Optix Aqua Focus N&D AV Oasys Purevision Biofinity Frequency ?
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Why decreased dryness in SiHy?
Low Dk of hydrogels leads to hypoxia Decreased corneal sensitivity, decreased tear flow Leads to inflammation and ocular surface damage Leads to lacrimal damage
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Lens Design Lathe-cut Cast molded Spun-cast
Lathe-cut back & spun-cast front
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Optics Aspheric lenses to optimize spherical clarity or correct spherical aberration Focus N&D, Air & O2 Optix, PureVision, Frequency Aspheric, Biofinity, Avaira
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FITTING Patient Selection
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Indications Spherical RE Inability to adapt to GP’s Low astigmats
Lenticular astigmatism Career enhancing Occasional wear Inability to adapt to GP’s Responsibility Motivation Chronic GP complications
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Low astigmats Spherical equivalent Soft Toric Aspheric design
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Career Enhancing Athletes Actors Models Eye Changing Tints
Fountain of Youth
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Responsibility Age restrictions Participation in the costs of the lens
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Variability in Lifestyle
Want to sleep overnight in their lenses on a regular basis Essentially every other SCL patient entering your office desires the freedom and flexibility of sleeping in their lenses, at least occasionally. 25% 54% 21% Don’t want to sleep in their lenses Want to sleep overnight in their lenses occasionally Source: CIBA Vision, data on file, 2005.
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Sleeping in lenses Most who sleep in their lenses do so frequently – average is 21 nights/month 41% of those sleeping in their lenses do so for more than 7 nights continuously Many (28%) are wearing lenses not approved for such use 84% of soft contact lens wearers accidentally fall asleep or nap with their lenses (Source: CIBA Vision, data on file)
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Contraindications Inflammation/Disease of Anterior Seg
Systemic disease Pregnancy Poor hygiene Lack of motivation Irregular cornea RK Chronic allergies Chronic use antihistamines GPC Astig.>1D Work environment Poor tears
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Systemic diseases Epilepsy Diabetes Mental incompetency
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Pregnancy complications
Dry eyes Refractive changes- Corneal thickness changes Decreased corneal sensitivity Increased tear viscosity
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Preliminary evaluation is important for determining patient suitability
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35 y.o male banker Desires CL’s for occasional sports activities
Case 1 35 y.o male banker Desires CL’s for occasional sports activities
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24 y.o female Wants CL’s 1st time 3 months pregnant
Case 2 24 y.o female Wants CL’s 1st time 3 months pregnant
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Auto mechanic Wants CL’s Poor hygiene
Case 3 Auto mechanic Wants CL’s Poor hygiene
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What is the patient interested in?
Lens Selection Lens Type DW, FW, EW, CW Replacement schedule Tints What is the patient interested in?
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DW, FW, EW, CW Wear 12-14 hours a day Remove daily
Occasional overnight wear Full time overnight wear 7 days/6 nights 30 day wear
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Educate and Set Proper Expectations- Making the switch
Oxygen Transmission Corneal Health Modulus Replacement schedule Discuss going from hydrogel EW to SiHy EW or CW Give the patient 1-2 weeks
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CW Patient Education Use appropriate solutions for SiHy’s
Rub the lenses to clean, except ClearCare Do not swim in lenses and do not sleep in lenses after swimming Clean & disinfect upon removal Need back-up glasses with updated Rx Examine every 6 mths. Bring glasses and solutions to visits Remove when ill and do not sleep in them Must be 100% healthy to wear CW Remove if dirty or FB sensation to clean & disinfect Replace with fresh, clean lenses each month Showering in lenses?
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Even in a BMW, you need to slow down when it is icy. -Dr. Ghormley
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CW Wearing Schedule New CL patient – Immediate CW
Follow-up: 1wk, 3wk, 6wk, 6mth DW SCL patient – 3 days DW, CW Follow-up: 10 days, 3 wk, 6wk, 6mth EW SCL patient – 1 week DW, CW Follow-up: 2wk, 3wk, 6wk, 6mth
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Replacement Schedule Daily Weekly Every 2 weeks Monthly Every 2 months
Quarterly Traditional/Conventional
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Tints Handling Enhancing Opaque Opaque wild & crazy
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Lens Inversion Markings
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BCR 4-5D flatter than flat K Steepest BCR = flat K >45D
Middle BCR = flat K 41-45D Flat BCR = flat K < 41D
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Lens Diameter HVID +2 = Lens Diameter mm
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Lens Power Vertex > + 4D Spherical equivalent for < 1D cyl
Residual astigmatism = Refractive cylinder
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Center Thickness Greater minus – Thinner Greater plus – Thicker
Thicker lenses are easier to handle Thinner lenses provide greater oxygen transmission
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Empirical vs. Diagnostic
Fitting Evaluation Empirical vs. Diagnostic
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Case 1 OU OD –2.00D OS – X180
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Case 2 OD 43.00 Sph. OS 42.50/43.50 @90 OD –4.50 OS –4.50-1.00X180
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Fitting Insert lenses and let settle 10-15 minutes
Assess position, coverage and movement Centration- centered Complete corneal coverage 0.5-1mm lag, Push-up test
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Too tight Conjunctival drag Negative push-up test No movement
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Too loose > 2mm lag Moving off cornea Decentered inferiorly
Edge lift Slides inferior on superior gaze
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Edge fluting
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Determine visual acuity and lens power by best sphere & sphero-cylindrical over-refraction
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Over-keratometry Flat Fit
Mire distortion which becomes more distorted on blink Steep Fit Clear mire on blink which becomes distorted
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Assess Patient Comfort
Dispense out of Inventory/Trials? Parameters required to order (BCR, Rx, Material name, diameter?, CT?, tint) Verify lens specifications prior to dispensing
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Follow-Up Evaluations
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Patient Education Provide written instructions
Don’t bombard them with info Give them nuggets Provide wearing schedule Teach I & R Provide Informed Consent Teach lens & case care Teach how to open blister pack
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Nuggets Use a rewetting drop prior to removal
Dial toric lenses prior to removal FB under lens, pull onto sclera and blink back on Use viscous solution like daily cleaner to unroll edges
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Lens Insertion tips Fingers dry Make sure lens is not inverted
Inspect lens Place on sclera or directly on cornea
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Lens Removal tips Slide the lens off onto sclera
Pinch off with the finger pads
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Informed Consent should cover:
Specifies patient taught I&R, care Emergency phone number Risks Dr. copy & patient copy
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Progress Evaluations Case Hx VA Over-Ks SLE lenses on & off
K’s with lenses off Refraction RTC schedule
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Case History Problems/complaints WT Solutions: Are they compatible?
Have they switched? Are they disinfecting, enzyming, cleaning? Are they compliant?
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SLE with lenses Clear, white eye Position Coverage Movement
Defects in the lens
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SLE without lenses Edema (microcysts, striae, polymegethism)
Neovascularization Limbal engorgement Injection Lid eversion Fluorescein Evaluation (Rinse out)
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Case 1 A patient is fit in a Frequency 55 lens, base curve radius of 8.4mm, worn DW. It is a group 4 lens with a water content of 55%. It comes in base curve radii of 8.4, 8.7 & RTC in 2 wks with trial lens. Upon the return visit, engorged limbal vessels and conjunctival drag. What do you plan to do?
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Case 2 Focus Monthly wearer, DW basis Group 4, BCR 8.6
Using Complete, appears compliant but has deposits Name other options for this patient?
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Case 3 Your patient works at a computer at work. She uses frequent rewetting drops. She experiences dryness. What might be helpful for her?
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Case 4 Patient is wearing AV lenses 2-3 weeks continuously. Some signs of edema. What lens options might you want to discuss with the patient?
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Case 5 Patient is interested in obtaining soft extended wear tinted bifocal toric lenses.
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Case 6 Patient had ocular trauma to the left eye which resulted in a large distorted pupil. The patient is unhappy with the cosmetic appearance. The iris color of the OD is blue.
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Case 7 Patient desires to wear soft lenses; however, he desires very little care regimen.
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Case 8 Patient is being fit for CL’s for the 1st time. She loves monovision; however, she has trouble seeing the lenses when handling. What would you do for her?
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Case 9 Patient was fit in Focus Night & Day. They previously wore AV 2 for 1-2 weeks EW. They return for a 1 week check. They are complaining of lens awareness. SLE findings are normal.
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Case 10 Patient is wearing PureVision lenses. At their 2 week follow-up visit you notice a mild coating on the lenses. The patient is using Aquify with their lenses. Any thoughts on what might be happening?
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