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Amplitude of accommodation (AA) is a measurement of the eye’s ability to focus clearly on objects at near distances (i.e. accommodation). This eye focusing range for a child is usually about 5–7.5 cm (2–3 inches). For a young adult, it is 10–15 cm (4–6 inches). The focus range for a 45-year-old adult is about 50 cm (20 inches). For an 80-year-old adult, it is 1.5 m (60 inches).
The average amplitude of accommodation, in diopters, for a patient of a given age may be estimated by Hofstetter's formula: 18.5 - (0.30 * patient age in years). The minimum amplitude of accommodation can likewise be estimated by: 15 - (0.25 * age in years), and the maximum amplitude of accommodation can be estimated by 25 - (0.40 * age in years)."