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The amplitude of accommodation is the maximum increase in optical power that an eye can achieve in adjusting its focus from as far as possible (beyond infinity for a longsighted eye) to the nearest possible. It confers a certain range of object distances for which the retinal image is as sharply focussed as possible.
Amplitude of accommodation is measured during routine eye-examination. The closest that a normal eye can focus is typically about 10 cm for a child or young adult. Accommodation then decreases gradually with age, effectively finishing just after age fifty.
The average amplitude of accommodation, in diopters, for a patient of a given age was estimated by Hofstetter in 1950 to be 18.5 - (0.30 * patient age in years) with the minimum amplitude of accommodation as 15 - (0.25 * age in years), and the maximum as 25 - (0.40 * age in years). However, Hofstetter's work was based on data from two early surveys which, although widely cited, used methodology with considerable inherent error.