100, 120 and other super high plus diopter lenses? WOW!

Discussion in 'Optometry Archives' started by acemanvx, Dec 30, 2005.

  1. acemanvx

    acemanvx Guest


    I never knew it was possible to make such high plus diopter lenses! I
    researched into this when my ophthamologist used a +90 diopter lense to
    look in my eyes. That thing was nearly spherical not unlike a marble!
    If one were to look into a lens with a dioptric value higher than the
    axial length of your eye, would light focus *outside* your eyeball? I
    know an emmetropic eyeball is +60 diopters and placing a plus lens
    makes light focus in front of the retina but as long as the lens is
    less than +60 light would come to a focus still inside your eye. How do
    the optics of a lens higher than +60 work if light now comes to a focus
    *outside* your eye? Would there be a difference between a +66, +78,
    +90, +100 or even +120? Would light of a super high plus come in focus
    at a point still inside the lens? Or right after it finishes traveling
    thru the lens? Would you be able to see clearly from 1cm away from your
    eyeball itself or 1cm away from the surface of the plus lens when its
    held to your eye? How high can plus lenses get really?
    acemanvx, Dec 30, 2005
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  2. Yes. The real, inverted image forms between the lens and the observer.
    This very common technique is called indirect ophthalmoscopy.

    Would there be a difference between a +66, +78,
    Yes. Image size and field of view. +20 D. lenses are only used with an
    opthalmoscope, 78 and 90 are only used with a slit lamp.
    William Stacy, Dec 30, 2005
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  3. acemanvx

    acemanvx Guest

    Thanks! So if one were to look thru say a +120d lense, would he be
    seeing everything upside down?

    Also whats the difference between dioptric value and magnification
    times? Take a magnifying glass lens thats marked as 10x for example or
    a microscope eyepiece marked as 10x, 15x, 20x or so? What dioptric
    value would such lenses have?
    acemanvx, Dec 30, 2005
  4. Yes, and it doesn't need to be that strong. You get the same effect if
    you hold any plus lens farther away from your eyes than it's focal length.
    approximately 4 D. per x mag. applies to single lens systems, with
    microscopes or other multiple lens systems you have to multiply the
    components. (gross simplification/approximation)
    William Stacy, Dec 30, 2005
  5. William Stacy wrote:

    You get the same effect if
    (providing the object viewed is also beyond the lenses' focal length)
    William Stacy, Dec 30, 2005
  6. acemanvx

    Salmon Egg Guest

    Salmon Egg, Dec 30, 2005
  7. In eye exams, +90 D lenses are used (although 78 is more common) in
    conjunction with a slit lamp biomicroscope to get a nice, although
    inverted, binocular view of the retina. Useful especially for fine 3-D
    viewing of the macula.

    I can't think of any use for 100 D or more single lenses.

    w.stacy, o.d.
    William Stacy, Dec 30, 2005
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