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List of soft contact lens materials
List of soft contact lens materials
List of soft contact lens materials
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Soft contact lenses are one of several types of contact lenses for corrective vision eyewear as prescribed by optometrists and ophthalmologists.[1]

Background

[edit]

In the US market, soft contact lenses are approved by the US Food and Drug Administration.[2] The American Optometric Association published a contact lens comparison chart called Advantages and Disadvantages of Various Types of Contact Lenses on the differences between them.[3] These include:

  • soft contact lenses
  • rigid gas-permeable (RGP)
  • daily wear
  • extended wear
  • disposable
  • planned replacement contact lenses.

The US Food and Drug Administration (FDA) defines soft contact lenses as:

made of soft, flexible plastics that allow oxygen to pass through to the cornea. Soft contact lenses may be easier to adjust to and are more comfortable than rigid gas permeable lenses. Newer soft lens materials include silicone-hydrogels to provide more oxygen to your eye while you wear your lenses.[4]

History

[edit]

The first contact lenses were made of glass, in 1888. Initially the glass was blown but soon lenses were made by being ground to shape. For the first fifty years, glass was the only material used. The lenses were thin, yet reports of injury were rare. In 1938 perspex (polymethylmethacrylate, or PMMA) began to replace glass in contact lens manufacture. PMMA lenses were easier to produce so the production of glass lenses soon ended. Lenses made of PMMA are called hard lenses.[5] Soft contact lenses were first produced in 1961 by Czech chemical engineer Otto Wichterle using polyhydroxyethylmethacrylate (pHEMA), a material that achieved long-term commercial application. Lenses made of polyacrylamide were introduced in 1971.[5]

Types

[edit]

The FDA classifies soft contact lenses into four groups for the US market. They are also subcategorized into 1st generation, 2nd generation, and 3rd generation lens materials.[6] These 'water-loving' soft contact lens materials are categorized as "Conventional Hydrophilic Material Groups ("-filcon"):

Group Water Content Percentage Ionic/Non-Ionic
I Low Water Content (<50%) Nonionic
II High Water Content (>50%) Nonionic
III Low Water Content (<50%) Ionic
IV High Water Content (>50%) Ionic

Note: Being ionic in pH = 6.0 – 8.0.[7]

The FDA has been considering updating soft contact lens group types and related guidance literature.[8][9][10]

Contact lens polymers

[edit]

The materials that are classified in the 5 FDA groups include the ones listed in the next 5 sections:[11][12]

FDA classification of soft contact lens materials[13]
FDA lens group Adopted name Transmissibility level

(Dk x10-11)

Water content Chemical composition
I
non-ionic
low water content 		galyfilcon A 60 47% –
lotrafilcon A 140 24% DMA, siloxane, TRIS
lotrafilcon B 110 33%
polymacon 7.5 36% HEMA
tetrafilcon 9.0 43.5% HEMA, MMA, NVP
II
non-ionic
high water content 		alphafilcon A 22.9 66% HEMA, NVP
hilafilcon A 26.9 70%
omafilcon A 19.6 62% HEMA, PC
III
ionic
low water content 		balafilcon A 99 36% NCVE, NVP, PBVC, TPVC
bufilcon A 16.0 45% DA, HEMA, MAA
IV
ionic
high water content 		etafilcon A 17.0 58% HEMA, MAA
ocufilcon D 19.7 55%
vifilcon A 16.0 55% HEMA, MAA, PVP
DA – diacetone acrylamide; DMA – N,N-dimethylacrylamide; HEMA – 2-Hydroxyethyl methacrylate; MAA – methacrylic acid; MMA – methyl methacrylate; NCVE – N-carboxl vinyl ester; NVP – N-vinyl pyrrolidone; PBVC – poly[dimethylsiloxyl] di[silybutanol] bis[vinyl carbamate]; PC – phosphorylcholine; TPVC – tris-(trimethylsiloxysilyl) propylvinyl carbamate; TRIS – tris-(hydroxylmethyl) aminomethane

Hydrogel groups

[edit]

Below is a list of most contact lens materials on the market, their water percentage, their oxygen permeability rating, and manufacturer brands.[14][15][16][17] Note that the higher the oxygen transmissibility rating, the more oxygen gets to the eye.

Low-water nonionic

[edit]
Material % Water Oxygen Transmissibility (Dk/t) Brands
Tefilcon 38 8.9 Cibasoft, Illusions, Torisoft, Softint, STD, LL Bifocal
Tetrafilcon A 43 9 Cooper Clear, Cooper Toric, Preference, Preference Toric, Vantage, Vantage Accents, Vantage Thin, Vantage Thin Accents
Crofilcon 38 13 CSI, CSI Toric
Helfilcon A/B 45 12 Continental Toric, Flexlens, Flexlens Toric, Flexlens Aphakic, Optima Toric, All X-Cel lenses
Mafilcon 33 4 Menicon
Polymacon 38.6 8.5–24.3 Allvue, Biomedics 38, Clearview, CustomEyes 38, EpconSOFT, EsstechPS, Esstech PSD, Esstech SV, Frequency 38, HD, HD-T, HDX, HDX-T, Horizon 38, Hydron Mini, Hydron Zero 4 SofBlue, Hydron Zero 6 SofBlue, Hydron Versa Scribe, Lifestyle MV2, Ideal Soft, Lifestyle Xtra, Lifestyle 4Vue, Lifestyle Toric Bifocal, LL38, Metrosoft ll Multifocal, Metrosoft Toric, Natural Touch, Occasions, Optima 38/SP, PS-45 Multifocal, Simulvue 38, Sof-form II, SofLens, SofLens38, SofLens Multi-Focal, Softics, SoftView, Unilens 38, Westhin Toric, EZvue Soft Contact Lens, Solotica
Hioxifilcon B 49 15 Alden HP Sphere, Alden HP Toric, Aquaease, Essential Soft Toric Multifocal, Flexlens, Quattro, Satureyes, Satureyes Toric and Multifocal, All X-Cel Lenses

High-water nonionic

[edit]
Material % Water Oxygen Transmissibility (Dk/t) Brands
Surfilcon A 74 35
Lidofilcon A 70 31 ActiFresh 400, CV 70
Lidofilcon B 79 38
Netrafilcon A 65 34.5
Hefilcon B 45 10 Optima Toric
Alphafilcon A 66 32 SofLens Toric for Astigmatism
Omafilcon A 58–60 28–36.7 Proclear 1-Day, Proclear EP, Proclear 1 day Multifocal, Proclear Multifocal Toric, Biomedics XC, Aveo
Omafilcon B 62 21.3–52.3 Proclear Sphere, Proclear toric, Proclear toric XR, Proclear multifocal, Proclear multifocal XR, Proclear multifocal toric
Vasurfilcon A 74 39.1 Precision UV
Hioxifilcon A 59 28 Alden HP Sphere, Alden HP Toric, ExtremeH₂O 59% Thin/Extra, Biocurve Gold Sphere and Toric, Aura ADM, Scout by Warby Parker,[18] Hydro by Hubble, Miru 1 Day[19]
Hioxifilcon D 54 21 Alden HP Sphere, Alden HP Toric, ExtremeH₂O 54%, Clarity H₂0, C-Vue Advanced Custom Toric
Nelfilcon A 69 26 Focus Dailies, Focus Dailies Toric/Progressive, Dailies AquaComfort Plus, FreshLook One-Day, Synergy, Triton
Hilafilcon A 70 35
Hilafilcon B 59 22 SofLens 59, SofLens Daily Disposable, SofLens Daily Disposables for Astigmatism
Acofilcon A 58 25.5 Flexlens Tricurve Keratoconus
Nesofilcon A 78 42 Biotrue ONEday

Low-water ionic

[edit]
Material % Water Oxygen Transmissibility (Dk/t) Brands
Bufilcon A 45 16 Hydrocurve II 45, Soft Mate B
Deltafilcon A 43 10 Amsoft, Amsoft Thin, Comfort Flex, Custom Flex, Metrosoft, Soft Form Toric
Phemfilcon 38 9 Durasoft 2

High-water ionic

[edit]
Material % Water Oxygen Transmissibility (Dk/t) Brands
Bufilcon A 55 16 Hydrocurve I, Hydrocurve 3 Toric, Softmate II
Perfilcon A 71 34 Permalens
Etafilcon A 58 23.8–28 Acuvue, Acuvue Bifocal, Acuvue 2, Acuvue 2 Colors, 1-Day Acuvue, 1-Day Acuvue Moist, 1-Day Acuvue Moist for Astigmatism, 1-Day Acuvue Moist Multifocal, 1-Day Acuvue Define, Colornova, Discon, Waldo, Natural Vue, Ocylens
Focofilcon A 55 16 Fre-Flex
Ocufilcon B 52–53 16–24 ClearSight 1-Day, Continental, Ocu-Flex 53
Ocufilcon C 55 16 UCL55, UCL-Pediatric
Ocufilcon D 55 17.8–28.1 Biomedics 55 Premier asphere, Biomedics Toric, ClearSight 1-Day Toric, Horien 1-Day Disposable
Ocufilcon E 65 22 Ocuflex 65
Ocufilcon F 60 24.3 Hydrogenics 60 UV
Phemfilcon A 55 16 Durasoft 3, Freshlook, Wildeyes
Methafilcon A 55 17.9-37.6 Biocurve Advanced Aspheric, Biocurve 1-Day, Biocurve Toric & Sphere, C-Vue 1-Day ASV, C-Vue 55, Edge III 55, Elite AC, Elite Daily, Elite AC Toric, Expressions Colors, Flexlens, Frequency 55 Sphere/Multifocal, HD2, HDX2, Horizon 55 Bi-Con, Hubble, Kontur, LL55, New Horizons, Revolution, Sauflon 55, Sof-form 55, Sunsoft Eclipse, Sunsoft Toric, Vertex Sphere, Vertex Toric
Methafilcon B 55 14.5–31.3 Frequency 55 Toric, Hydrasoft Sphere, Hydrasoft Sphere Thin, Hydrasoft Aphakic, Hydrasoft Aphakic Thin, Hydrasoft Toric, Hydrasoft Toric Thin
Vilfilcon A 55 16 Focus 1–2 Week Softcolors, Focus Monthly Softcolors, Focus Toric, Focus Progressives, Soft 55, Soft 55 EW

Silicone hydrogel polymers

[edit]
Material FDA Group % Water Oxygen Transmissibility (Dk/t) Modulus (MPa) Center Thickness (mm) Brands
Lotrafilcon A 1 24 175[20] 1.5 0.08 Air Optix Night & Day Aqua
Lotrafilcon B 1 33 110–138 1.0 0.08 O2Optix, Air Optix for Astigmatism, Air Optix Aqua, Air Optix Aqua Multifocal, Air Optix Colors
Galyfilcon A 1 47 86[21] 0.43 0.07 Acuvue Advance with Hydraclear, Acuvue Advance for Astigmatism
Senofilcon A 1 38 103–147 0.7 0.07 Acuvue Oasys, Acuvue Oasys for Astigmatism, Acuvue Oasys for Presbyopia, Acuvue Oasys 1-Day, Acuvue Oasys 1-Day for Astigmatism, Acuvue Oasys with Transitions, Acuvue Oasys Max 1-Day, Acuvue Oasys Max 1-Day Multifocal
Senofilcon C 41 129–147 0.77 0.07 Acuvue Vita, Acuvue Vita for Astigmatism
Sifilcon A 1 32 82 0.08 O2Optix Custom
Comfilcon A 1 48 116–160 0.75 0.08 Biofinity, Biofinity toric, Biofinity XR, Biofinity XR toric, Biofinity Energys, Biofinity multifocal
Enfilcon A 1 46 100 0.6 0.06 Avaira, Avaira Toric
Balafilcon A 3 36 91-130 1.1 0.09 PureVision, PureVision Toric, PureVision Multi-Focal, PureVision2, PureVision2 for Astigmatism, PureVision2 Multi-Focal for Presbyopia
Delefilcon A 33–99
(water gradient)		 156[22] 0.7 0.09 Dailies Total1, Dailies Total1 Multifocal, DailiesTotal1 for Astigmatism
Narafilcon B 1 48 55 1-Day Acuvue TruEye (old)
Narafilcon A 46 118 0.66 0.085 1-Day Acuvue TruEye (new)
Stenfilcon A 54 80–100 0.4 0.08 MyDay, MyDay toric, MyDay Multifocal, Kirkland Signature
Somofilcon A 56 57–86 0.5 0.07 Clariti 1 day, Clariti 1 day toric, Clariti 1 day multifocal, Live daily disposable
Fanfilcon A 55 90–110 0.6 0.06 Avaira Vitality, Avaira Vitality toric, 24H Toric
Samfilcon A 46[23] 163[24] 0.7 0.07 Bausch & Lomb Ultra, Bausch & Lomb Ultra for Astigmatism, Bausch & Lomb Ultra for Presbyopia
Elastofilcon 0.2 340 SilSoft Aphakic, SilSoft Super Plus
Kalifilcon A 55 134[25] 0.5 0.08 Bausch & Lomb INFUSE
Asmofilcon A 40 161[26] 0.9 0.08 Miru 1month
Verofilcon A 51–80
(water gradient) 		100 0.6 0.09 Alcon Precision1, Alcon Precision1 for Astigmatism
Lehfilcon A 55–99
(water gradient) 		154[27] 0.6 0.08 Total30
Olifilcon B 47
 120[28] 0.6 0.08 Kits Daily, Everclear Elite, Hubble SkyHy
Olifilcon A 47
 150[29] 0.6 0.08 Everclear Plus, Everclear Air

Production generations

[edit]

There are three generations of silicone hydrogel contact lens materials:[30]

1st Generation 2nd Generation 3rd Generation
Material: Lotrafilcon A, Balafilcon A Senofilcon A, Galyfilcon A Samfilcon A, Comfilcon A, Enfilcon A, Asmofilcon A[31]
Features: TRIS structures, plasma treated, high modulus Modified Tanaka monomer, lack of coatings, higher Dk for water content No TRIS structure, no surface treatments or wetting agents, breaks traditional water-Dk-modulus relationships

References

[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

List of soft contact lens materials

View on Grokipedia
from Grokipedia
Soft contact lenses are fabricated from hydrophilic polymers that absorb water to form flexible, oxygen-permeable materials, primarily categorized as conventional hydrogels or silicone hydrogels, enabling comfortable wear directly on the eye for vision correction. These materials are classified by the U.S. Food and Drug Administration (FDA) into four groups based on water content—low (<50%) or high (≥50%)—and ionicity (non-ionic or ionic), a system designed to evaluate compatibility with lens care solutions and ensure biocompatibility and safety. Group 1 comprises low-water, non-ionic hydrogels like polymacon, offering durability but lower oxygen transmission; Group 2 includes high-water, non-ionic types such as ocufilcon B for enhanced comfort; Group 3 features low-water, ionic polymers like lidofilcon B, balancing wettability and deposit resistance; and Group 4 encompasses high-water, ionic materials like etafilcon A, prized for superior hydration but prone to lipid deposition. The foundational polymer for hydrogels is poly(2-hydroxyethyl methacrylate) (pHEMA), developed in the 1960s through copolymerization of 2-hydroxyethyl methacrylate (HEMA) with cross-linkers like ethylene glycol dimethacrylate (EGDMA), achieving water contents of 20-80% for flexibility and biocompatibility. Silicone hydrogels, introduced in the late 1990s, incorporate polydimethylsiloxane (PDMS) or tris(trimethylsiloxy)silylpropyl methacrylate (TRIS) with hydrophilic monomers like N-vinylpyrrolidone (NVP) or methacrylic acid (MAA), dramatically increasing oxygen permeability (Dk >100 barrers) to support extended wear while maintaining modulus values of 0.2-2 MPa for handling ease. Silicone hydrogels have evolved through three generations, with third-generation materials incorporating advanced wetting agents for better comfort. Notable advancements include surface modifications with (PEG) or poly(vinyl alcohol) (PVA) to improve wettability and reduce protein adsorption, as well as the development of materials like nelfilcon A (PVA-based) for daily disposables emphasizing natural tear-like hydration. As of 2024, silicone hydrogels dominate the market, accounting for 64% of lens fittings due to their superior oxygen permeability.

Background

Historical Development

The development of soft contact lens materials originated in the late 19th century with Adolf Fick's invention of the first functional contact lens in 1888, a large glass scleral design intended to correct severe astigmatism by resting on the sclera rather than the cornea. This early prototype, though uncomfortable and limited to short wear times, laid the groundwork for subsequent innovations in ocular correction. In 1936, Czech chemist Otto Wichterle advanced the field by creating the first rigid contact lenses from polymethyl methacrylate (PMMA), a transparent plastic that offered greater durability and lighter weight than glass, enabling corneal rather than scleral fitting. The breakthrough for soft lenses occurred in 1961 when Wichterle, collaborating with Drahoslav Lim, developed the first prototype using poly(2-hydroxyethyl methacrylate) (pHEMA), a hydrophilic polymer capable of absorbing up to 40% water to mimic the eye's natural moisture and improve comfort. This material allowed lenses to conform flexibly to the , reducing irritation associated with rigid designs. Commercialization followed in 1971 with FDA approval of Bausch & Lomb's Soflens, the first mass-produced soft lens made from polymacon (a pHEMA variant), which rapidly gained popularity for daily wear despite initial challenges in manufacturing and durability. Key advancements in the included the introduction of high-water content (over 50% water), which enhanced wearer comfort and initial oxygen flow to the , alongside the FDA's establishment of a four-group classification system for these materials based on water content and ionic properties. By the late , limitations in oxygen permeability of traditional prompted the integration of silicone into formulations, creating silicone that significantly improved gas transmissibility while maintaining softness. The first such lens, lotrafilcon A (used in CIBA Vision's Focus Night & Day), received FDA approval in 1998, enabling safer extended wear. The early 2000s saw further growth in extended wear capabilities, highlighted by the 2001 FDA approval of the Night & Day lens for up to 30 nights of continuous use, reducing risks of hypoxia-related complications. As of 2025, over 25 years after the commercialization of hydrogels, these materials had become predominant, accounting for approximately 75% of new soft lens fittings worldwide due to their superior performance in daily and overnight applications.

Key Properties and Metrics

Soft contact lens materials are evaluated based on several core physical properties that influence their performance, safety, and user comfort. , expressed as the percentage of water in the fully hydrated lens, typically ranges from 30% to 80% and plays a critical role in determining lens flexibility, oxygen transport to the , and overall wearing comfort; higher generally enhances comfort by improving conformability to the eye but can increase evaporative if not balanced with adequate . Another related metric is the pervaporation rate, which quantifies the evaporation of water from the ocular environment through the contact lens, combining permeation and evaporation processes. While useful for assessing evaporation-related comfort, particularly at low humidity, the pervaporation rate has limitations when comparing contact lenses: it addresses only dehydration-induced discomfort and does not encompass overall performance or eye health; oxygen transmissibility (Dk/t) is more critical for preventing complications such as corneal edema and hypoxia; other factors, including surface wettability, elastic modulus, deposition resistance, and on-eye dehydration kinetics, also significantly influence comfort; furthermore, in vitro measurements do not always predict real-world performance due to variations in tear composition, blink rate, and environmental conditions. Materials are further classified as ionic or nonionic depending on the presence of charged functional groups, such as sulfonic or carboxylic acids in ionic hydrogels, which attract oppositely charged proteins and from the tear film, leading to higher deposition risks and potential discomfort or reduced lens lifespan in ionic types compared to nonionic ones. Oxygen permeability is a key metric for ensuring corneal , quantified by the Dk value, which measures the intrinsic ability of the to transmit oxygen and is expressed in units, where 1 equals 10^{-11} (cm³ STP·cm)/(cm²·s·cmHg). The effective oxygen transmissibility, Dk/t, accounts for lens thickness (t in cm) and is reported in barrers/cm, with values above 24 typically recommended for daily wear to minimize corneal and hypoxia, though higher thresholds like 87 are advised for extended wear to prevent overnight swelling. This shift toward higher Dk became prominent in the to address limitations in traditional hydrogels. Mechanical properties, including the , assess the material's stiffness and handling characteristics, with lower values (often 0.3–1.0 MPa or approximately 40–145 psi) preferred for enhanced on-eye comfort and reduced lid interaction during . Wettability, evaluated via the formed between the lens surface and a saline droplet, indicates tear film stability; advancing contact angles below 90° signify good surface hydration and resistance, preventing dryness and deposits that could impair vision. The U.S. (FDA) groups materials into four categories based on and ionicity to guide and care recommendations: Group I (low water, <50%, nonionic) offers low deposition but limited oxygen flow; Group II (high water, >50%, nonionic) balances comfort and moderate permeability; Group III (low water, ionic) offers similar oxygen permeability to Group I but higher protein buildup; and Group IV (high water, ionic) maximizes hydration yet poses the greatest deposition risk, often requiring enzymatic cleaners. These properties are standardized under ISO 18369, which outlines measurement protocols for parameters like (via gravimetric methods), Dk (polarographic or coulometric techniques), modulus (), and (goniometry), ensuring consistent evaluation across materials.

Hydrogel Groups

Low-Water Nonionic (Group I)

Low-water nonionic soft contact lenses, classified as FDA Group I, feature water contents below 50% and lack ionic charges in their structure, which minimizes attraction to and proteins from the tear film. This composition makes them particularly suitable for sensitive eyes, as they exhibit reduced buildup of deposits compared to ionic or higher-water materials. Key materials in this group include polymacon, hefilcon A, and tetrafilcon A, each offering distinct mechanical and tailored for daily wear. Polymacon, a primarily based on 2-hydroxyethyl (HEMA), has a water content of 38.6% and oxygen transmissibility (Dk/t) ranging from 8.5 to 24.3, depending on lens power and thickness, with a modulus of approximately 0.8 MPa that contributes to its firmness. Hefilcon A, composed of HEMA and N-vinyl-2-pyrrolidone (NVP), provides 42% water content and Dk/t values between 10 and 20, balancing hydration with structural integrity. Tetrafilcon A, a terpolymer of HEMA, NVP, and , achieves 43.5% water content with a Dk of around 9, supporting moderate oxygen flow while maintaining lens stability. These materials offer high durability and resistance to deformation, making Group I lenses ideal for first-time wearers who require straightforward handling and minimal maintenance. Their nonionic nature also slows dehydration in dry environments, reducing discomfort for users with mild dry eye symptoms. However, the lower results in reduced relative to high-water groups, potentially limiting extended wear suitability and necessitating careful monitoring for corneal . Commercial examples include Bausch + Lomb's SofLens 38 lenses made from polymacon, often prescribed for biweekly or monthly replacement schedules to optimize hygiene and comfort. Older formulations of CooperVision's Focus and Precision brands utilized tetrafilcon A or similar Group I polymers, typically on monthly cycles, while hefilcon A appears in specialty tinted lenses like Saview-Colors Aqua 42 UV, suited for similar replacement intervals.

High-Water Nonionic (Group II)

High-water nonionic soft contact lenses, classified as FDA Group II, feature a water content exceeding 50% and lack ionic charges, enabling enhanced hydration for wearer comfort while minimizing protein deposition compared to ionic counterparts. These materials strike a balance by offering superior initial comfort through increased flexibility and moisture retention, though they may dehydrate more rapidly in low-humidity environments due to their elevated water levels. Key examples of Group II materials include nelfilcon A, omafilcon A, and nesofilcon A, all nonionic hydrogels designed for daily wear. Nelfilcon A, found in Dailies AquaComfort Plus, exhibits a higher of 69% with a Dk/t of 26 at -3.00D, prioritizing surface hydration via crosslinking. Omafilcon A, used in Proclear lenses, has 62% , a Dk/t of 51 at -3.00D, and a modulus of 0.6 MPa, providing good oxygen flow and resistance to dehydration. Nesofilcon A, in Biotrue ONEday, achieves 78% with a Dk of 42, emphasizing high hydration mimicking the tear film for all-day comfort.
MaterialWater ContentDk/t (at -3.00D)Modulus (MPa)Example Lens
Nelfilcon A69%26Not specifiedDailies AquaComfort Plus
Omafilcon A62%510.6Proclear
Nesofilcon A78%60Not specifiedBiotrue ONEday
These materials offer advantages such as improved wettability and slightly higher oxygen permeability over low-water nonionic (Group I) lenses, facilitating better all-day comfort without the deposition risks associated with ionic groups. However, some formulations exhibit higher modulus values, which can enhance handling durability but may feel less soft on insertion compared to ultra-high-water options. Commercial applications focus on daily disposable formats for daily wear, exemplified by AquaComfort Plus (nelfilcon A), which incorporates wetting agents like for blink-activated refreshment and reduced end-of-day dryness. Similarly, Proclear (omafilcon A) and Biotrue ONEday (nesofilcon A) support short-term use with high hydration and aspheric designs for visual clarity in everyday scenarios.

Low-Water Ionic (Group III)

Low-water ionic soft contact lens materials, classified as FDA Group III, consist of hydrogels with less than 50% water content and ionic components, often incorporating charged groups such as those derived from to facilitate water binding at physiological . These materials exhibit a higher propensity for protein deposition compared to nonionic counterparts due to electrostatic interactions with tear proteins, but they demonstrate robust mechanical strength, making them suitable for durable lens designs that withstand handling and wear. Oxygen transmissibility (Dk/t) in these materials typically ranges from 10 to 20, supporting moderate oxygen needs for daily wear and select extended wear scenarios without excessive corneal stress. Representative examples of Group III materials include crofilcon and lidofilcon B, both with low water contents around 38%, offering balanced properties for extended wear applications. Crofilcon, used in older lenses like CSI, has a Dk/t of 13 and modulus approximately 1.0 MPa, providing good durability for correction. Lidofilcon B features a Dk/t of about 18, contributing to its use in lenses requiring moderate breathability. These properties position Group III materials for monthly replacement schedules and toric designs addressing .
MaterialWater Content (%)Dk/tModulus (MPa)Example Lenses
Crofilcon38131.0CSI, CSI Toric (older extended wear)
Lidofilcon B3818N/ABiomedics-related designs
The ionic composition enhances tear stability through improved hydration layers, promoting longer wear comfort in moderate environments, while the low minimizes risks for users in dry conditions or with mild dry eye. However, the charged surface increases and protein buildup, often necessitating enzymatic cleaners to prevent discomfort and maintain clarity during extended use. Commercial monthly options, such as older Biomedics designs using lidofilcon B, leverage these traits for reliable performance.

High-Water Ionic (Group IV)

High-water ionic soft contact lenses, classified by the FDA as Group IV, are hydrogel materials containing more than 50% water by weight and incorporating ionic monomers such as methacrylic acid, which impart a negative charge to the polymer. These lenses are particularly suited for wearers with dry eyes, as the elevated water content enhances initial comfort and wettability upon insertion, mimicking the eye's natural moisture levels. However, the ionic nature combined with high hydration makes them susceptible to greater protein and lipid deposition from the tear film, necessitating rigorous cleaning regimens and often limiting their use to daily or short-term replacement schedules. Representative materials in this group include etafilcon A and ocufilcon D, which exemplify the balance of softness and oxygen transmission typical of Group IV polymers. Etafilcon A, a of 2-hydroxyethyl (HEMA) and (MAA), features 58% and an oxygen transmissibility (Dk/t) of 28 at -3.00D, with a low modulus of approximately 0.5 MPa contributing to its supple feel. Ocufilcon D, used in daily disposable formats like Biomedics 55, has 55% and a Dk/t of 28 at -3.00D, offering similar ionic characteristics with balanced oxygen flow.
MaterialWater Content (%)Dk/t (at -3.00D)Modulus (MPa)Key Features
Etafilcon A5828~0.5High wettability, UV protection; prone to deposits
Ocufilcon D5528~0.6Daily disposable compatible; balanced comfort
These materials provide superior initial softness and oxygen permeability compared to lower-water groups, as water acts as the primary oxygen carrier in hydrogels, supporting corneal health during daily wear. The high water content also facilitates better dehydration resistance in humid environments, reducing end-of-day dryness for sensitive eyes. Conversely, the ionic charge attracts more tear proteins and lipids, increasing the risk of buildup that can cause discomfort or reduced vision clarity, which is why extended wear is generally not recommended without specialized care. Commercial examples of Group IV lenses include the Acuvue 2 biweekly replacement lenses made from etafilcon A, which emphasize comfort for correction, and daily disposables like 1-Day Acuvue Moist and Biomedics 55 (ocufilcon D), available in multifocal designs to address while minimizing deposit accumulation through frequent replacement. These products highlight the group's role in frequent-replacement modalities, prioritizing all-day hydration for users with demanding visual needs.

Silicone Hydrogel Polymers

First Generation

The first generation of hydrogel materials, introduced between 1998 and 2003, represented a pivotal advancement by integrating components, such as tris(trimethylsiloxy)silyl propyl (TRIS), with traditional polymers to achieve significantly higher oxygen permeability (Dk) while maintaining sufficient hydration for comfort. These materials typically featured water contents ranging from 24% to 36% and were characterized by relatively high mechanical , with moduli exceeding 1.0 MPa, which contributed to their durability but also posed handling challenges. Developed primarily by CIBA Vision (now ) and , these lenses addressed the oxygen limitations of conventional s, enabling safer extended wear schedules. FDA approvals for daily wear began in 1997, with extended wear clearances following in 2001 for key products. Key examples include lotrafilcon A, used in Focus Night & Day (later Air Optix Night & Day Aqua) lenses by CIBA Vision, which has a 24% , Dk of 140 barrers, Dk/t of approximately 140, and modulus of 1.2 MPa. Balafilcon A, employed in Bausch & Lomb's PureVision lenses, offers 36% , Dk of 91 barrers, Dk/t of 99, and modulus of 1.1 MPa. These materials were the first to support true extended wear up to 30 continuous days, reducing hypoxia-related complications like corneal swelling compared to traditional hydrogels. However, their higher modulus and hydrophobic surfaces often led to reduced wettability, increasing risks of ocular dryness and giant papillary (GPC) due to mechanical irritation and protein deposition.
MaterialWater Content (%)Dk (barrers)Dk/tModulus (MPa)Example BrandFDA Approval Year (Extended Wear)
Lotrafilcon A241401401.2Focus Night & Day2001
Balafilcon A3691991.1PureVision2001
Note: Dk/t values are approximate for standard center thickness of -3.00D.

Second Generation

The second generation of silicone hydrogel contact lenses emerged between 2004 and 2008, building on the high oxygen permeability of first-generation materials by incorporating internal agents or surface coatings to enhance while maintaining Dk/t values in the range of 80 to 150. These lenses typically featured water contents around 33% to 47%, with reduced modulus compared to earlier hydrogels to improve lens flexibility and wearer comfort. Key innovations included the use of hydrophilic polymers like (PVP) as internal wetting agents, which migrated to the lens surface to promote tear film stability and reduce deposition. Representative materials from this generation include senofilcon A, galyfilcon A, and lotrafilcon B, each developed by major manufacturers to address the stiffness and dryness issues of prior designs. The following table summarizes their core properties:
MaterialBrand ExampleWater Content (%)Dk/t (at -3.00D)Modulus (MPa)
Senofilcon AAcuvue Oasys (Johnson & Johnson)381470.7
Galyfilcon AAcuvue Advance (Johnson & Johnson)47860.6
Lotrafilcon BAir Optix (Alcon)331380.75
These properties were verified through manufacturer specifications and independent testing, with senofilcon A and galyfilcon A utilizing Hydraclear technology—a PVP-based internal agent—for sustained hydration, while lotrafilcon B employed plasma surface treatment to enhance wettability. The primary advantages of second-generation silicone hydrogels were improved all-day comfort and reduced end-of-day dryness, attributed to lower modulus values that allowed better conformity to the ocular surface and the incorporation of agents that minimized and . Clinical studies demonstrated up to 10-20% better subjective comfort scores compared to first-generation lenses during extended wear. However, some materials exhibited residual surface in low-humidity environments without additional coatings, potentially leading to minor deposit accumulation over time. Commercially, led with senofilcon A and galyfilcon A in products like Acuvue Oasys (launched 2005) and Acuvue Advance (2004), while introduced lotrafilcon B in Air Optix (2006), expanding the category to include toric and multifocal designs by 2008 to accommodate and . This period marked a shift toward daily wear preferences, with over 50% for by 2008.

Third Generation

The third generation of materials emerged around , building on prior innovations by incorporating higher water contents of 46-80% and advanced smart surface designs, such as water gradients, to improve wettability and reduce end-of-day discomfort without relying on external coatings or plasma treatments. These materials prioritize biomimetic properties that mimic the natural tear film, achieving oxygen transmissibility (Dk/t) greater than 100 while maintaining a low modulus below 0.6 MPa for enhanced flexibility and lens handling. This generation addresses key comfort limitations from earlier , such as deposition and dryness, through internal hydrophilic modifications that promote stable hydration throughout wear. Key examples of third-generation materials include comfilcon A, used in CooperVision's Biofinity line, with 48% , Dk/t of 116, and modulus of 0.5 MPa; samfilcon A, featured in Bausch + Lomb's Ultra lenses, offering 46% , Dk/t of 114, and modulus of 0.6 MPa; delefilcon A, employed in Alcon's Total1, which has a core of 33% increasing to 80% at the surface for a Dk/t of 156 and modulus of 0.5 MPa; and enfilcon A, introduced in 2011 for CooperVision's Avaira, with 46% and Dk/t of 103. These formulations emphasize a balance of high oxygen flow and low stiffness to support extended wear while minimizing mechanical irritation to the ocular surface.
MaterialBrand ExampleWater ContentDk/tModulus (MPa)
Comfilcon ABiofinity ()48%1160.5
Samfilcon AUltra ()46%1140.6
Delefilcon A Total1 ()33% core / 80% surface1560.5
Enfilcon AAvaira ()46%1030.5
The primary advantages of these materials lie in their biomimetic surface architectures, which create a highly hydrated outer layer to minimize evaporative dryness and , resulting in reduced dropout rates among wearers experiencing discomfort. Despite these benefits, the sophisticated processes lead to higher production costs, potentially increasing retail prices for consumers. Post-2020 updates have focused on toric variants, such as enhanced delefilcon A designs in Alcon's Total1 for , providing improved rotational stability and all-day moisture retention without compromising . Commercially, third-generation materials power leading product lines from and , which together capture significant market segments through innovations in moisture-retaining technologies like embedded wetting agents. As of 2024, silicone hydrogels overall account for over 70% of new soft lens fittings, reflecting their dominance in addressing modern demands for comfort and health in extended-use scenarios.

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