This is a question regarding lens effectivity. Specifically, this question tests whether you know how the power of a lens will change as you move the lens further from the eye. The basic premise is this:

To calculate the new effective power of this plus lens, you need to calculate the new focal length:

new focal length = old focal length - distance moved from eye

new focal length = 0.2 m - 0.020 m = 0.180 m

Thus, the effective power of this +5.00 diopter lens is really 1 / 0.180 =

**+5.56 diopters**. You know you have to

**subtract** the distance moved from the old focal length since the new effective lens power has to be

**more positive**.

The change in magnification is simply the ratio of the new effective lens power to the original lens power:

change in magnification = 5.56 / 5.00 =

**1.11**Please note that this question is

**NOT **asking you to calculate the power of the spectacles that would be needed given his contact lens prescription. That type of question is also a very common question that is asked on board exams. In that latter case, you would need a

**weaker** plus power spectacle since it is effectively stronger further from the eye. The power of this spectacle would be: 1 / (0.2 + 0.02) = +4.55 diopters.