How big is our normal blind spot?

Discussion in 'Optometry Archives' started by CGeorge, Jul 12, 2006.

  1. CGeorge

    CGeorge Guest

    How big is it if you look at things from, let's say, a 5 yard distance?
    CGeorge, Jul 12, 2006
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  2. CGeorge

    serebel Guest

    Close your eyes and it's huge. :)
    serebel, Jul 13, 2006
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  3. CGeorge

    Don W Guest

    You really should be talking about subtended angles. The blind spot is 5
    degrees wide and 7 degrees high according to Bennett and Rabbetts. An old
    astronomer's trick for measuring angles is the width of a closed fist at
    arm's length is 10 degrees. So my question is, how are you measuring the
    blind spot?

    Don W.
    Don W, Jul 14, 2006
  4. CGeorge

    Don W Guest

    Exactly how did you do that?

    Don W.
    Don W, Jul 14, 2006
  5. CGeorge

    Don W Guest

    If I take the conventional 3" x 5" card and put a "dot" and a "+" on it
    (couple of inches apart) to check the blind spot, I get the "+" to disappear
    at about 8 inches looking at the "dot" . Now if I just run a vertical line
    thru the "+" to cover the entire card, I can get the "+" to disappear, but
    the line stays intact continuous, but no horizontal part of the "+").
    Interesting computational fill in. So if you are looking at a 10" book at 5
    feet, that covers 9 degrees, which exceeds the blind spot dimension. So I
    would say it was lucky your book disappeared.

    Don W.
    Don W, Jul 14, 2006
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