The<unk>  is the maximum potential increase in optical power that an eye can achieve in adjusting its focus. It refers to a certain range of object distances for which the retinal image is as sharply focussed as possible.<unk>  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.<unk>  then decreases gradually with age, effectively finishing just after age fifty. The average<unk> , 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<unk>  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. (Donders, Sheard, Duane, Turner for reference)
Amplitude of accommodation
Basal rate
Dark adaptation threshold
Optokinetic response
Positive relative accommodation
Negative relative accommodation
Intermuscular coherence
Threshold potential