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Simplified Accommodation Model

Though the real eye is a two-lens system operating into a water-like medium (see scale model eye), it is instructive to model accommodation with a single 50 diopter lens treated as if it were operating in air. If this simplified eye is forced to accomodate from infinity to 25 cm it can give some insight into the nature of nearsigntedness and farsigntedness and their corrections.
Focusing at infinity with a 50 diopter lens gives 2 cm as the lens-to-retina distance. Using the thin lens equation and an object distance of 25 cm yields a required accommodated lens strength of about 54 diopters, an 8% accommodation range.
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