Low Vision Question

Discussion in 'Optometry' started by yOyOYoo, Dec 14, 2008.

  1. yOyOYoo

    yOyOYoo Member
    7+ Year Member

    Oct 3, 2003
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    A hand-held magnifier has a power of +10 D. When used by an unaccommodated emmetrope it is held at a distance of 20cm from his eyes. What is the relative distance mag (or effective mag for 40 cm reference distance)? Can the patient vary the distance of the magnifier from his eye? What happens to the magnification if he holds it at 30 cm? what happens to the field of view at 30 cm?

    Any low vision gurus out there? I could use a little help... thanks
  2. alferec

    alferec Future Army OD
    5+ Year Member

    Dec 9, 2004
    Likes Received:
    Optometry Student
    I'm not giving the answer since that's making things too easy for you...but I can help you out.

    If based off 40 cm:
    Relative distance magnification = Equivalent Power รท 2.50 D

    If you can figure out the equivalent power of a hand magnifier system without an add, then you can figure out the relative distance mag.

    To find out the last two parts of the question, take out one of your plus trial lenses (or any other plus lens really) and hold the lens to some text. Keep that distance constant while moving your head farther away then closer, then you can figure out how the field of view and magnification changes.
    Stop hovering to collapse... Click to collapse... Hover to expand... Click to expand...

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