Amplitude of Accommodation
Optics and Optometry
Hofstetter's expected range for an age, alongside the push-up and minus-lens measurements.
How it is calculated
- Hofstetter's three equations, in dioptres: minimum = 15 − 0.25 × age, expected = 18.5 − 0.30 × age, maximum = 25 − 0.40 × age.
- The minimum line is the clinically useful one — an amplitude below it is the definition of accommodative insufficiency for that age.
- Push-up measurement: the amplitude is the reciprocal of the near point in metres. A near point of 10 cm is 10.00 D.
- Minus-lens measurement: the strongest minus lens cleared, plus the demand of the test distance, conventionally less 0.25 D for the minification the lenses themselves introduce.
- Hofstetter fitted these lines to two early surveys, and later work on much larger samples finds all three sit above modern measurements. They remain what is taught and examined, which is why they are here, but a measured amplitude should always win.
- Each line crosses zero at a different age, between 60 and 62.5. Past that the equation is extrapolating beyond its own data and the tool clamps it at zero rather than reporting a negative amplitude.
References
- Hofstetter HW. A useful age-amplitude formula. Optometry and Vision Science 1950;38:42-45.
- Anderson HA, et al. — subsequent analyses find Hofstetter's equations overestimate measured amplitude across large samples.
About these tools
OcuLearning Clinical Tools is part of an educational platform. These calculators are provided for learning and reference, and are not medical advice, a diagnosis, or a treatment recommendation.