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2016 Material Science Series “The Chemistry of Sight: Material Innovations in Eye Care and Contact Lenses”
Mark Jones
Heather Sheardown
Executive External Strategy and Communications Fellow, Dow Chemical
Professor, Department of Chemical Engineering, McMaster University
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THE CHEMISTRY OF SIGHT: MATERIAL INNOVATIONS IN EYE CARE AND CONTACT LENSES
Heather Sheardown
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The Eye
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Contact Lenses • 100 million contact lens wearers worldwide • 1.4% of population but only 4% of 2.4 billion people who wear glasses • To be accepted, contact lenses need to be simpler, more convenient and very very comfortable
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Contact Lenses 3 types of lenses commonly used •
Rigid gas permeable lenses
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Soft hydrogel lenses
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Silicone hydrogel lenses
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Desirable Properties of Contact Lenses • Ability to correct vision • Comfort in the eye • Low deposition of tear components • Mechanical properties (resistance to tear) • Oxygen permeability
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Soft Contact Lenses • Developed early 60s – originally from poly (hydroxyethyl methacrylate) • Made from slightly crosslinked hydrophilic polymers •
Polymers added to alter water uptake which determines oxygen permeability
• Generally thought to be very comfortable but limited wear time due to low oxygen permeability
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Typical Soft Contact Lenses
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Rigid Gas Permeable Lenses • Introduced in the late 70s • Show high oxygen permeability but lack comfort • Copolymers of PMMA and silicone containing materials – typically methacryloxypropyltris(trimethyoxy) silane + hydrophilic comonomers to impart hydrophilic character to the lenses • Development of fluorine containing RGP lenses based on realization that the fluoroderivatives may improve oxygen permeability and resistance to deposit formation on lenses
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Composition of RGP Lenses
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Silicone Hydrogel Contact Lenses • Recognition of outstanding oxygen permeability of silicone rubber • Oxygen transport occurs through the silicone phase rather than water phase as with traditional soft contact lenses • Silicone elastomers on their own stick to the cornea • Combine HEMA with monomer so successfully used in the manufacture of RGP lenses
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Co-Continuous Phases • Combination of adequate oxygen permeability and adequate ionic or hydraulic permeability • Macromer + TRIS + Solvent, one of which is a hydrophilic monomer
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Co-Continuous Phases • Combination of adequate oxygen permeability and adequate ionic or hydraulic permeability
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Monomers Used in Silicone Hydrogel Manufacture
TRIS 26
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TRIS Modifications
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Macromers for Silicone Hydrogels
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Comparison of Properties of First Two Silicone Hydrogels
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Oxygen Permeability
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Audience Survey Question ANSWER THE QUESTION ON BLUE SCREEN IN ONE MOMENT
About how many people worldwide wear contact lenses? • 75 million people
• 105 million people • 115 million people • 130 million people • 150 million people
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CL Wearers • CL’s represent the most widely used biomaterial worldwide • Worn by 130 million people
– 32 million in US – 3.5 million in Canada • 90% wear SCL
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Growth in SiHy Materials
Morgan et al, CL Spectrum 2016; 31(1): 28-33
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Current Issues with Contact Lenses • Protein and lipid adsorption • Rigidity • Surface friction • COMFORT
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Intraocular Lens Implants •
10 million IOLs are implanted annually in developed world and developing countries
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Cataracts remains the leading cause of blindness worldwide
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The Lens •
The lens is situated behind the iris in a small bag-like structure called the lens capsule
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The lens itself is generally considered to be composed of three layers, appropriately titled the lens nucleus, the lens cortex and the lens epithelium ANTERIOR
epithelial cells
cortical fibres POSTERIOR
nuclear fibres
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DISTANCE VISION low power lens relaxed ciliary muscle
cornea NEAR VISION high power lens
contracted ciliary muscle
cornea
Audience Survey Question ANSWER THE QUESTION ON BLUE SCREEN IN ONE MOMENT
When was the first Intraocular Lens (IOL) surgery performed? • 1938 • 1949 • 1954 • 1967 • 1971
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Current Technologies to Treat Cataracts •
Dr. Harold Ridley is credited with performing the first IOL operation on November 29, 1949
•
He chose polymethyl methacrylate as the his material choice as he observed it induced a negligible tissue response in the eye while working as a military surgeon
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Current Materials and Designs • Hydrophobic acrylic materials • Hydrophilic acrylic materials • Silicones • Square edged design
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In Bag Positioning
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Phakoemulsification
© 2008
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Progression of IOL Materials
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Problems with Current Technologies •
Approximately 30% of patients with artificial intraocular lenses (IOLs) develop posterior capsule opacification (PCO) within five years of surgery and must undergo a subsequent procedure
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Currently there are only 3 accommodative IOLs on the market and none effectively reduces the incidence of PCO
© 2008
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Lens Refilling •
During this technique, the capsular bag is evacuated through a small capsular opening to be then refilled with an elastic polymer capable of responding to adequate change in surface curvature according to the varying zonular tension.
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In Situ Curable Silicones – Example • • • •
Used ROP to create prepolymers using D4 and D4H Hexaethyldisiloxane used as a cap to control molecular weight Used hydrosilation to create polymerizable groups Cured by UV polymerization within 5 min
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Drug Delivery to the Eye •
Eye disease is becoming a greater burden on society – Aging population – Increased incidence of health problems – Increased incidence of psychological problems
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New treatments developed based on increased understanding of biological mechanisms
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Challenge is delivery to the target tissue
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Opportunity Pharmacological treatments for back of the eye diseases are a growth industry
Source: Braun Consulting group
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Problem Biological barriers limit treatment options Both eye drops and systemic administration of drug fail to reach target site at therapeutic concentrations Recurring injection is the status quo Painful, invasive, potentially dangerous, low patient compliance Drug delivery devices are transforming the market Controlled release devices are seen as the next step
Iluvien from Alimera Sciences
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Audience Survey Question ANSWER THE QUESTION ON BLUE SCREEN IN ONE MOMENT
What percentage of the drug actually gets to the desired target in the eye with topical drops? • About five percent • About ten percent • About twenty percent • About thirty percent • About fifty percent
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Topical Drops • 90% of current market formulations for disease management – poor insertion technique in >50% • over-spill
– – – –
poor compliance in 50% tear flow drainage diluted by blinking corneal diffusion resistance
• Substantial systemic absorption •
