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To the Editor.
—To facilitate remembering the amplitude of accommodation (AA) vs age in years, I have derived the following Rule of Fours for the benefit of your subscribers:
Ages 4 through 40:
(1) AA (diopters) =
Ages 41 through 49:
(2) AA (D) = 4 - 0.4(Age - 44)Rules of Fours 1 and 2 are of most practical value for ease of memory and application and are the best approximate mean values for the sake of simplicity.
Ages greater than 49 up to 59:
The preceding rules were derived by (3) AA (D) = 2 - 0.1(Age - 49) piecewise continuous linear analysis of Donders' data as modified by Duane1 for a lens which is placed before the emmetropic eye at a distance of 14 mm from the cornea (ie, the anterior focus of the eye as a reference point). Please note that age 4 and not age 8 was chosen as a starting
Kern SP. "RULE OF FOURS". Arch Ophthalmol. 1971;86(3):360. doi:10.1001/archopht.1971.01000010362020