What is Hofstetter's formula for the minimum amplitude of accommodation?

• A. 15 - 1/4(age)
• B. 18.5 - 1/3(age)
• C. 25 - 0.4(age)
• D. 20 - age

Answer: (A)

Accommodative power tends to decline with age, and Hofstetter gave practical age-based estimates to describe typical ranges. For the minimum amplitude of accommodation, the model is 15 minus a quarter of age, measured in diopters. This means younger individuals are predicted to have a higher minimum AA, and as age increases, the minimum expected AA decreases by 0.25 D each year. For example, at age 20 the minimum would be about 10 D, and at age 60 it would approach 0 D.

Hofstetter also provides two related reference formulas: an average amplitude of 18.5 minus 0.3 times age, and a maximum amplitude of 25 minus 0.4 times age. These give a range of what’s typical for a given age, with the minimum representing the lower bound of normal.

So the correct expression for the minimum amplitude of accommodation is 15 minus 0.25 age.