Article Date: 7/1/2010

Soft Contact Lenses

Soft Contact Lenses

Hydrogel and Silicone Hydrogel Lens General Considerations

The FDA gives each contact lens material a generic name. In general, all hydrogel and silicone hydrogel lens generic names end in the suffix “filcon” and all nonhydrogel lenses end in “focon.”

Hydrogel lenses are categorized into four groupings for purposes of evaluating effects of accessory products upon the lens material. Lenses with less than 50 percent water content are considered to be “low water” and the others are “high water.” Less reactive surfaces are termed “nonionic” and more reactive materials are labeled “ionic.” Silicone hydrogel lenses are low water.

Disinfection of hydrogel and silicone hydrogel lenses can usually be done safely and effectively by approved chemical or hydrogen peroxide systems. However, some Group 4 ionic polymers may react negatively with potassium sorbate- or sorbic acid-preserved solutions.

In the term Dk, D stands for diffusion and k for solubility. The oxygen permeability of hydrogel lenses is almost entirely the result of solubility and for GP materials almost entirely the result of diffusion. In silicone hydrogel materials, oxygen permeability is a combination of solubility and diffusion, with the larger amount from diffusion. That is, the hydrogel component in the formulation provides solubility and the silicone component provides diffusion. Each generic material below is accompanied by a representative Dk number.

A clinically useful approximation is to consider Dk values for hydrogel lenses in three groups:

H20 Dk
38±%
55±% 18±
75±% 36±

It is also important to remember that Dk/t (central transmissibility) and Dk/t (average overall transmissibility) are dependent upon contact lens thickness configuration and are more important than Dk with hydrogel lenses. With silicone hydrogel contact lenses, Dk/t and Dk/t are more similar than with hydrogel lenses.

This table should assist you in identifying specific lenses in each category as related to disinfection and Dk; and it will also help you determine an appropriate mix of lens types for your practice.

GROUP 1

Low Water (<50% H20)
Nonionic Hydrogel Polymers

tefilcon (38%) (Dk = 8.9)

tetrafilcon A (43%) (Dk = 9)

crofilcon (38%) (Dk = 13)

helfilcon A&B (45%) (Dk = 12)

mafilcon (33%) (Dk = 4)

polymacon (38%) (Dk = 9)

  • 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
  • PS-45 Multifocal
  • Simulvue 38
  • Sof-form II
  • Soflens
  • Soflens 38
  • Soflens Multifocal
  • Softics
  • SoftView
  • Unilens 38
  • Westhin Toric
  • hioxifilcon B (49%) (Dk = 15)

    Note: All X-Cel lenses are available in helfilcon A, hioxifilcon A, hioxifilcon B, and methafilcon A.

    Silicone Hydrogel Polymers

    lotrafilcon A (24%) (Dk = 140)

    lotrafilcon B (33%) (Dk = 110)

    galyfilcon A (47%) (Dk = 60)

    narafilcon B (48%) (Dk = 55)

    senofilcon A (38%) (Dk = 103)

    sifilcon A (32%) (Dk = 82)

    comfilcon A (48%) (Dk = 128)

    enfilcon A (46%) (Dk = 100)

    GROUP 2

    High Water (>50% H20)
    Nonionic Hydrogel Polymers

    lidofilcon A(70%)(Dk = 31)

    alfafilcon A (66%) (Dk = 32)

    omafilcon A (59%) (Dk = 33)

    vasurfilcon A (74%) (Dk = 39.1)

    hioxifilcon A (59%) (Dk = 28)

    hioxifilcon D (54%) (Dk = 21)

    nelfilcon A (69%) (Dk = 26)

    hilafilcon B (59%) (Dk = 22)

    acofilconA(58%)Dk = (25.5)

    GROUP 3

    Low Water (<50% H20)
    Ionic Hydrogel Polymers

    bufilcon A (45%)(Dk = 16)

    deltafilcon A (43%)(Dk = 10)

    phemfilcon A (38%) (Dk = 9)

    Silicone Hydrogel Polymers

    balafilcon A (36%) (Dk = 112)

    GROUP 4

    High Water (>50% H20)
    Ionic Hydrogel Polymers

    bufilcon A (55%) (Dk = 16)

    perfilcon (71%) (Dk = 34)

    etafilcon A (58%) (Dk = 28)

    focofilcon A (55%) (Dk = 16)

    ocufilcon B (53%)(Dk = 16)

    ocufilcon C(55%)(Dk = 16)

    ocufilcon D (55%) (Dk = 19.7)

    ocufilcon E (65%) (Dk = 22)

    ocufilcon F (60%) (Dk = 24.3)

    phemfilcon A (55%) (Dk = 16)

    methafilcon A (55%) (Dk = 18)

    methafilcon B (55%) (Dk = 18)

    vilfilcon A (55%)(Dk = 16)

    Spherical Clear and Visibility Tint Disposable and/or Planned Replacement Hydrogels

    Disposable and/or Planned Replacement Tinted Enhancer and Opaque Hydrogels

    Toric Disposable and/or Planned Replacement Hydrogels

    Multifocal Disposable and/or Planned Replacement Hydrogels

    Daily Wear Spherical Clear and Visibility Tint Hydrogels

    Extended Wear Spherical Clear and Visibility Tint Hydrogels

    Therapeutic Spherical Clear and Visibility Tint Hydrogels

    Aphakic Spherical Clear and Visibility Tint Hydrogels

    Special Design Spherical Clear and Visibility Tint Hydrogels

    Daily Wear Tinted Enhancer and Opaque Hydrogels

    Customized Tinting

    Adventures In Color Technology, Alden Optical, Crystal Reflections, Custom Color Contacts, Specialty Tint, and Ciba Vision Special Eyes Program provide custom tinting of soft contact lenses for prosthetic and other uses. For specific information, call them. Their telephone numbers and addresses are listed in the company directory at the end of this booklet.

    Marietta Vision states that the Chromagen lens is available for certain color deficiencies. It has a 5mm to 7mm tinted optic zone and custom parameters. Call (866) 300-6257 for details.

    Extended Wear Tinted Enhancer and Opaque Hydrogels

    Daily Wear Toric Hydrogels

    Extended Wear Toric Hydrogels

    Daily Wear Multifocal Hydrogels

    Extended Wear Multifocal Hydrogels

    Multifocal Toric Hydrogels

    Hybrid Soft Skirt/GP Center



    Contact Lens Spectrum, Issue: July 2010