Whats so great about silicone-hydrogels?

Discussion in 'Optometry Archives' started by crb, Jun 18, 2005.

  1. crb

    crb Guest

    why are they safer

    I had lousy luck with comfort with the first ones I tried last year. I
    wish I
    remember the exact model I had.

    Are their newer ones out to try?
     
    crb, Jun 18, 2005
    #1
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  2. crb

    LarryDoc Guest

    1. 4 to 12 times the oxygen permeability of older tech lenses (depends
    on how old the tech and which current silicone material). The high level
    of oxygen reaching the cornea eliminates tissue swelling, engorgement of
    the capillaries surrounding the cornea and the potential for
    neovascularization (new blood vessels growing where they should not) and
    allows for rapid healing of minor cornea surface damage. This in turn
    reduces the risk of infection.
    2. material does not foster bacteria/virus growth on the surface which
    reduces potential for infection.
    3. material does not dehydrate on the eye and change fitting
    configuration.
    4. surface far more resistant to deposits, although some si-hydros will
    deposit lipids but generally less so than older tech lenses.
    5. material more eye tissue compatible for most people.
    6. material does not "soak up" chemical residues from lens care products
    or that which is dissolved in tears following exposure to atmospheric
    contamination.

    In short, silicone hydrogels, IMHO and that of many others, makes all
    other soft lens plastics obsolete. Silicone hydrogel lenses mark the
    first significant change on soft contact lens chemistry in a decade, and
    the previous change was minor in comparison, so perhaps the first real
    change in 25 years.

    A year ago there was only one lens on the market in the USA. (Not so
    elsewhere.) Today, there are four: (in particular order: Acuvue Advance,
    Purevision, O2Optix, Focus Night&Day.) There will likely be two more
    coming sometime soon.

    --LB, O.D.
     
    LarryDoc, Jun 18, 2005
    #2
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  3. crb

    kemccx Guest

    I'll reply as a patient who's been trying to find the right contact
    lens after not wearing them for many years. I find the silicone
    hydrogel lens very comfortable, but the vision is less than acceptable
    for me. I'm not sure why that is. The OD is perplexed as well, since
    my slight astigmatism should not affect the results to that degree.
    So, I keep going back to the Biomedics 55, where the vision is better.
    Karen
     
    kemccx, Jun 18, 2005
    #3
  4. crb

    Dr. Leukoma Guest

    Karen, I have seen this as well. I think the reason is that the
    silicone hydrogels, because of their elastic modulus, do not drape as
    well. As a result there might be some vaulting of the lens over the
    cornea which changes the focus with every blink. I have recently been
    through this exercise with one of my patients. Pehaps switching to a
    flatter base curve will help.

    DrG
     
    Dr. Leukoma, Jun 19, 2005
    #4
  5. crb

    kemccx Guest

    Interesting. He gave me another trial lens to use - at a higher
    prescription it's a -6.0, 8.6 , 13.8 - which is the base curve value?
    And, if it's the last number, is it flatter than a 14.2 ? All my
    other lenses have been 8.6 and 14.2. Thanks
    Karen
     
    kemccx, Jun 19, 2005
    #5
  6. crb

    Dr. Leukoma Guest

    I can only hope that future posters will provide the technical details
    first.

    The base curve is 8.6, the diameter is 13.8. I can tell from this that
    you are wearing the Focus N&D. For this lens, 8.6 is the flatter of
    the two available base curves. The Focus N&D has the lowest water
    content and the highest elastic modulus. It is very stiff. Is this
    the lens you were complaining about in your first post? The only other
    available silicone hydrogel lens in a flatter base curve is the Acuvue
    Advance. It has a higher water content, and a correspondingly lower
    elastic modulus.

    DrG
     
    Dr. Leukoma, Jun 19, 2005
    #6
  7. crb

    crb Guest

    1. 4 to 12 times the oxygen permeability of older tech lenses (depends
    on how old the tech and which current silicone material). The high level
    of oxygen reaching the cornea eliminates tissue swelling, engorgement of
    the capillaries surrounding the cornea and the potential for
    neovascularization (new blood vessels growing where they should not) and
    allows for rapid healing of minor cornea surface damage. This in turn
    reduces the risk of infection.
    2. material does not foster bacteria/virus growth on the surface which
    reduces potential for infection.
    3. material does not dehydrate on the eye and change fitting
    configuration.
    4. surface far more resistant to deposits, although some si-hydros will
    deposit lipids but generally less so than older tech lenses.
    5. material more eye tissue compatible for most people.
    6. material does not "soak up" chemical residues from lens care products
    or that which is dissolved in tears following exposure to atmospheric
    contamination.

    In short, silicone hydrogels, IMHO and that of many others, makes all
    other soft lens plastics obsolete. Silicone hydrogel lenses mark the
    first significant change on soft contact lens chemistry in a decade, and
    the previous change was minor in comparison, so perhaps the first real
    change in 25 years.

    A year ago there was only one lens on the market in the USA. (Not so
    elsewhere.) Today, there are four: (in particular order: Acuvue Advance,
    Purevision, O2Optix, Focus Night&Day.) There will likely be two more
    coming sometime soon.

    --LB, O.D.
    [/QUOTE]
    Great information. Since I have Focus now maybe I'll try the Sil. Hyd.
    focus.
    Whatever Sil. Hy. the eyedoctor tried on me about 7 months ago was very
    uncomfortable.
    Felt like my eyes were dried out but they weren't. Almost painful and I
    had the urge to close my
    eyes.
     
    crb, Jun 21, 2005
    #7
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