Principle
With full distance correction in place the accommodation amplitude (AA) in Diopters can be calculated from the Near Point by the following formula:

AA in Diopter = 100 / dist in cm of near point

In order to determine the near point a visual target consisting of optotypes equivalent to J2 of the Jaeger’s near vision chart is brought close to the eye. The distance from the eye of the point when the subject reports beginning of “Blurring” of the optotypes is recorded and the corresponding Diopteric reading is noted from the scale on the instrument. In order to eliminate the influence of image size on the reading, attempt is made to take readings at a range of 15 to 40 cm from the eye. This is achieved by “drawing” the near point closer with the addition of convex lens in cases with poor accommodation and “pushing” the near point away with the addition of concave lens of known Diopteric power. This “additional” power is subtracted from the Diopteric reading to give the final AA.

[For example: If the accommodation amplitude read off the scale is 3.8 D and a +2.0 D addition has been placed in front of the subject’s full distance correction for the measurement, then the “net” Reading of 1.8 D (3.8 - 2.0) is taken as the AA.]

Once the AA is obtained in a subject the near point can be determined by using the formula:

Near point (cm) = 100 / AA in Diopter

[e.g. if the AA is 1.8 D then the near point is 55.6 cm.]