Low Vision Question

[yOyOYoo]

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

 

[alferec]

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 ÷ 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.