Shocking Clarity: Reading thru a small hole

Discussion in 'Optometry Archives' started by Fidelis K, Jan 19, 2007.

  1. Fidelis K

    Fidelis K Guest

    Background: I had cataract surgery in my good eye last year and the vision
    is set for 16." I wear -2.50 glasses with little bit of astigmatism
    correction (-.75, 170) for distance vision. When my doc tried that
    astigmatism correction with no spherical correction to see if my near vision
    could improve, my near vision became less clear. So, I & my doc decided that
    I wear nothing for reading. After all, my near vision, tested with a reading
    card, is 20/20.

    Last night, I was reading a book and happened to momentarily read it through
    my wedding ring. I noticed something and did some experiment. When I was
    reading through a small hole (1/4 inch diameter or so), print looked
    extremely sharp and ultra clear. I was completely amazed. I continued the
    same experiment, holding various books and newspapers at 16" distance &
    reading normally and through a small hole. The same result.

    So, my questions are, "Why does reading through a small hole make such a
    difference?" & "Does it mean that there is room for improvement in my near
    vision?" I'll see my doc next month and I want to be armed with some
    questions for him regarding this. Thanks.
     
    Fidelis K, Jan 19, 2007
    #1
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  2. Fidelis K

    Mark A Guest

    What you are describing is how an aperture works on a camera, and how it
    changes the amount of light and the depth of focus of an image on a film
    plane.
    http://en.wikipedia.org/wiki/Aperture
     
    Mark A, Jan 19, 2007
    #2
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  3. I'm suspicious of what you are describing; it doesn't add up. True, a
    pinhole will give you sharp vision, but you should be getting sharp
    vision with that eye without any Rx at near, or if the astigmatism is
    indeed blurring you, that weak pair should have worked. So I'm thinking
    that astigmatism Rx is off. Unless, perchance you were talked into
    getting a multifocal IOL in which case yes, the pinhole effect will
    clear the horrible optics of those terrible IOLs. Unfortunately, it's
    not too pleasant to have to wear pinhole glasses. Or, per another
    chance, were you doing this on your "bad" eye?

    w.stacy, o.d.
     
    William Stacy, Jan 19, 2007
    #3
  4. Fidelis K

    Fidelis K Guest

    My description is true and that's why I'm so puzzled. I have an Alcon
    monofocal (didn't want to take a chance with multifocals and don't mind
    wearing glasses) and I think the astigmatism Rx is more or less correct.
    I've had several post-ops and the astigmatism Rx has been the same.

    So, I guess there are two possibilities.

    1. My doc tried a wrong astigmatism Rx for my near vision.
    2. Or, astigmatism of my near vision is different from that of my distance
    vision <-- Is this possible?
     
    Fidelis K, Jan 20, 2007
    #4
  5. It is #1. #2 is not possible.

    w.stacy, o.d.
     
    William Stacy, O.D., Jan 20, 2007
    #5
  6. Fidelis K

    Salmon Egg Guest

    I only understand a bit of this paragraph.
    Ah! 16. " means 16" .
    A 1/4 inch hole is LARGE for this kind of test. Your eye's pupil is not
    likely to have opened up that much unless you are in pretty dark environment
    that would make reading difficult. A 1/16 inch or smaller hole seems to me
    to be a more realistic size. What it indicates to me is that you do not have
    a good prescription or that your eye is aberrated to the extent that you
    cannot get sharp vision. How big is your pupil?

    What a small hole does is to limit the area of the eye's optical system
    thereby avoiding the most aberrated portion of the eye. If by chance your
    pupil is indeed larger than 1/4 inch, the outer part of the eye lens and
    cornea will contribute most of the spherical aberration. That would be
    avoided by using the hole. It is this spherical aberration that degrades the
    visual acuity when your eyes are dilated for examination.

    I am not medically trained. I resort to my knowledge of optical physics to
    reach my opinion.

    Bill
    -- Fermez le Bush--about two years to go.
     
    Salmon Egg, Jan 20, 2007
    #6
  7. Fidelis K

    Dan Abel Guest

    This is a well known optical fact. If you just turn up the light, your
    pupil will constrict and you will have a natural small hole. This might
    well help with your astigmatism, as well as your other vision.
     
    Dan Abel, Jan 20, 2007
    #7

  8. Or it can hurt, as when you have a CENTRAL opacity, on which fact is
    based the BAT (brightness acuity test)

    w.stacy, o.d.
     
    William Stacy, O.D., Jan 20, 2007
    #8
  9. Fidelis K

    Dan Abel Guest

    Hadn't thought about that, and didn't know about the BAT. When I had
    cataract, I guess that is what I had? On second thought, no.
     
    Dan Abel, Jan 20, 2007
    #9
  10. Most cataracts that are operated for have some central opacity. The
    test really is for those who have sufficient clear lens periphery to do
    ok in low light but who are essentially "blinded by the light" of the
    BAT. It's how you can often justify cataract surgery on someone who has
    20/20 vision.
     
    William Stacy, O.D., Jan 20, 2007
    #10
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