Menu

Near point and accommodation calculator

Convert near point and focusing power, see the normal range for an age, and estimate a reading add.

Calculator

Near point and accommodation

Accommodation is the eye's focusing power for close-up. Convert near point ↔ diopters, see what is normal for an age, and estimate a reading add.

An eye on the left and a ruler in centimeters with the near point and reading distance marked The closer the near point is to the eye, the more focusing power (accommodation) the eye has. 0 25 50 75 100 cm from the eye near point reading
Distances are measured from the eye (with distance glasses on, if needed).
Measured by moving small print closer until it just blurs (the push-up test).
Words used here
Accommodation
The eye's own focusing for near: the lens inside the eye gets rounder to add plus power.
Amplitude of accommodation
The most focusing power the eye can add, in diopters. It shrinks with age (presbyopia).
Near point
The closest point the eye can see clearly while focusing as hard as it can. Amplitude (D) = 100 ÷ near point (cm).
Add
Extra plus power for reading (bifocals, progressives, readers). Only the eye doctor prescribes it; this is a study estimate.

Works on your device: nothing you type is saved or sent anywhere.

The formulas

  • Amplitude of accommodation (D) = 100 ÷ near point (cm). A near point of 25 cm means 4.00 D of focusing.
  • Focusing needed at a distance (D) = 100 ÷ distance (cm). Reading at 40 cm needs 2.50 D.
  • Hofstetter's expected amplitude by age: minimum 15 − 0.25 × age, average 18.5 − 0.3 × age, maximum 25 − 0.4 × age. At 40: 5.00, 6.50 and 9.00 D.
  • Add estimate (keep half in reserve): add = focusing needed − half the amplitude. At 40 cm with a 2.00 D amplitude: 2.50 − 1.00 = +1.50 D.

These assume the person is wearing their full distance correction. The add is always set by the eye doctor; this is a way to understand where the number comes from.

References

  • Hofstetter HW. A useful age-amplitude formula. Optometric World 1950;38:42–45 (quoted in Benjamin WJ, ed. Borish's Clinical Refraction).
  • Benjamin WJ, ed. Borish's Clinical Refraction. Butterworth-Heinemann (amplitude of accommodation, near point and the add).
  • Brooks CW, Borish IM. System for Ophthalmic Dispensing. Butterworth-Heinemann (near addition and working distance).

Calculators are study aids. Always verify finished eyewear with your instruments and follow your practice's procedures. More optical calculators.

Independent study resource

Not affiliated with or endorsed by ABO-NCLE, IJCAHPO, or any state board. Not medical advice. Practice questions are original and don't guarantee a passing score. Verify current requirements with the official source. Read the full disclaimer.