can any buddy suggest me how to calculate IOl power in Silicon filled eyes

Discussion in 'Eye-Care' started by ani, Aug 27, 2006.

  1. ani

    ani Guest

    HI
    Can any optometrist suggest me how to calculate IOLpower in silisocn
    filled eyes
    PLz tell me
     
    ani, Aug 27, 2006
    #1
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  2. ani

    Guest

    Dear Ani,

    The eye is not filled with silicon.

    The refractive index of the eye is about 1.33.

    The APPROXIMATE power of the lens of the eye is
    about 10 diopters.

    The total power of the eye is about 60 diopters.

    Otis
     
    , Aug 27, 2006
    #2
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  3. ani

    Guest

    Dear Ani,

    The eye is not filled with silicon.

    The refractive index of the eye is about 1.33.

    The APPROXIMATE power of the lens of the eye is
    about 10 diopters.

    The total power of the eye is about 60 diopters.

    Otis
     
    , Aug 27, 2006
    #3
  4. ani

    Jan Guest

    ani schreef:
    Look for Gullstrand's schematic eye.

    Be aware of the differences in refraction index and the differences in
    optical system build up.

    Jan (normally Dutch spoken)
     
    Jan, Aug 27, 2006
    #4
  5. ani

    Jan Guest

    schreef:
    Indeed, when we speak of a normal healthy eye.
    A bad and to simple statement Otis, you certainly have no knowledge what
    so ever in optics.

    refractive index tears 1,333

    refractive index fluid eye chamber and corpus vitreum 1,336

    refractive index cornea 1,376

    refractive index lens crystallina cortical-nuclear 1,386-1,406

    If that was true there are almost no myopic's anymore and a lot of plus
    lens fan's instead.

    No Otis, again you show your lack in optics, especially optics in eyes.

    BTW, the lens crystallina when replaced by an implant lens should,
    roughly said, have a power of 20 diopters.

    Otis, beat a retread.

    Free to Marcus Porcius Cato's "Ceterum censeo Carthaginem esse delendam"

    In conclusion, I think that the "old plus lens junk recovered by Otis"
    should be destroyed.

    Jan (normally Dutch spoken)
     
    Jan, Aug 27, 2006
    #5
  6. ani

    Guest

    What I said was the AVERAGE refractive index for the
    over-all eye was about 1.38 for an eye with a length
    of 24 mm. Different eyes will have different lengths,
    and different values of refractive index. Your is
    an idealization of a large number of eyes, and
    an analysis of a "frozen" eye -- for the convenience]
    of optical analysis. But it NEVER represents
    the dynamic behavior of the natural living eye.

    Otis
     
    , Aug 27, 2006
    #6
  7. ani

    Guest

    Dear Friend,

    You have made an assumption. That the natural eye is
    filled with silicon. This is not the case.

    In general, when a lens is removed (catarack surgery), the
    power of the eye is reduced by about 10 diopters.

    The power of the eye is about 60 diopters (different with
    different people), but the result of removing that
    internal lens is the need of a +10 diopter plus
    for clear focus AFTER the lens is removed.

    These values are approximate. Using ultra-sound
    methods -- better judgment may be made of the
    power of the internal lens -- and the necessary
    repacement.

    Otis
     
    , Aug 27, 2006
    #7
  8. ani

    Simon Dean Guest

    You're a fruitcake Otis. He never made that assumption. You're assuming
    that's what he's talking about.

    Get some sleep Otis.
     
    Simon Dean, Aug 27, 2006
    #8
  9. ani

    Ann Guest

    How do you know? A medical procedure fills the eye with silicon but
    you state that it doesn't..

    Ann
     
    Ann, Aug 27, 2006
    #9
  10. ani

    Ann Guest

    No. You have made an assumption that the OP is talking about a normal
    eye. A medical procedure can fill the eye with silicon but you are
    totally ignorant of that fact.. you are disgusting

    Ann
     
    Ann, Aug 27, 2006
    #10

  11. You would have to know the refractive index of the IOL for starters. And
    your question may have no possible answer.

    For example if you are using an IOL with the same index or less than
    that of the silicone oil, the power would be infinitely large, as no
    matter how strong it is in air, it will have a zero or negative power in
    a medium of the same index (unless the eye were very long, as in high
    myopia).

    Assuming an IOL of higher index than the oil, you need to know the
    corneal curvature and the axial length of the eye. From that, ordinary
    optical formulas will give you a power for the IOL, but remember you
    must correct for the power in air if the IOL is to be specified as
    measured in air.

    Of course no matter what you do, according to otis, the eye will adapt
    and emmetropize itself so long as you never put a minus lens in front of
    it, so I guess it doesn't matter what you put in there...

    Who needs a cornea or an IOL anyway, since the fundamental eye will
    always fix itself if left alone through the mystery of dynamic nature?

    w.stacy, o.d.
     
    William Stacy, Aug 27, 2006
    #11
  12. ani

    Jan Guest

    schreef:
    And you think the OP has no brains too?
    Yes and I'm the pope.

    Again Otis, this shows your lack in knowledge when it comes to optics.
    Wrong again Otis and again showing your lack in eye optic knowledge
    That's more like it.

    Otis, beat a retread.

    Free to Marcus Porcius Cato's "Ceterum censeo Carthaginem esse delendam"

    In conclusion, I think that the "old plus lens junk recovered by Otis"
    should be destroyed.

    Jan (normally Dutch spoken)
     
    Jan, Aug 27, 2006
    #12
  13. ani

    Jan Guest

    schreef:
    There is no such thing as an average refractive index of the eye Otis,
    only you make such a homemade brew.
    So are your's.

    But it NEVER represents
    Indeed, it only gives a average view on the optical topics concerning
    the eye (in rest, no accommodation) kicking and alive.

    Remember Otis, you and you alone are suggesting the eye is a simple
    box-camera.

    We know better.

    Otis, beat a retread.

    Free to Marcus Porcius Cato's "Ceterum censeo Carthaginem esse delendam"

    In conclusion, I think that the "old plus lens junk recovered by Otis"
    should be destroyed.

    Jan (normally Dutch spoken)
     
    Jan, Aug 27, 2006
    #13
  14. ani

    Jan Guest

    William Stacy schreef:
    I like your "dynamic" and "funda - mental" thoughts.

    Jan (normally Dutch spoken)
     
    Jan, Aug 27, 2006
    #14
  15. Yeah, and Jan I wish I'd paid more attention in Latin class. Thanks for
    your humor.

    BTW have you noticed that otis posts to the alt.cancer.breast group? He
    claims that brasierres cause it because everyone who gets it has had a
    bra on. Except otis. He is protected by the plus lens so is able to
    wear one with impunity...

    w.stacy, o.d.
     
    William Stacy, Aug 27, 2006
    #15
  16. ani

    ani Guest

    I mean was people who under go for silicon oil insertion in their for
    prevent retinal detachment so If they want to go for catract Sx how to
    calculate IOL power calculation in these patient. becoz For caculating
    we need to hav an axial length so the we usually ultrasound for
    caculation of axial length but here Refractive index differ so device
    caculates worng axial length so how do u caculate an axial length
    length ultimately how u calculate IOL power .............. that my
    question......
     
    ani, Sep 3, 2006
    #16
  17. you should take a look at:

    http://doctor-hill.com/iol-main/silicone.htm

    Seems prudent to use a flat rear curve which should not be influenced by
    the index of whatever is in the vitreous cavity. But if a biconvex iol
    is used, you would have to correct for the posterior curve using normal
    thick lens formulas:


    http://scienceworld.wolfram.com/physics/ThickLensFormula.html

    w.stacy, o.d.
     
    William Stacy, Sep 3, 2006
    #17
  18. ani

    Don W Guest

    A question moreso in the area of lens design than anything. It seems that
    the refractive material adjacent to the 'flat rear curve" would affect the
    focal point. The different entering angles, and angles thru the lens,
    (i.e., ray traces) would be then be refracted differently at the flat
    surface depending on the index of refraction. Would this not be the case?

    Don W.
     
    Don W, Sep 3, 2006
    #18
  19. No it wouldn't. An optically flat interface has no refractive power by
    definition.

    w.stacy, o.d.
     
    William Stacy, Sep 3, 2006
    #19
  20. ani

    Don W Guest

    Had wondered about this. In order for the flat to have "no refractive
    power" the rays must be close to the optical axis. That is, for the
    "definition" to hold, the input ray angles (radians) are the same as the
    trig equivalents. But my first guess is this is not true of images
    projected onto the retina.

    Don W.
     
    Don W, Sep 8, 2006
    #20
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