Students of physiologic optics, and this includes more or less every ophthalmologist, must have noted certain apparent discrepancies in the calculation of dioptric power as given in different works on the subject. For instance, in the classic work of Tscherning, the powers of the four refractive surfaces of the eye are given as follows:
Anterior surface of cornea, plus 47.24 diopters
Posterior surface of cornea, minus 4.73 diopters
Anterior surface of crystalline lens, plus 6.13 diopters
Posterior surface of crystalline lens, plus 9.53 diopters
These results are obtained by taking the reciprocal of the first focal length of each of these surfaces, the focal lengths being calculated from the given radii and indexes. The powers can be directly obtained by using my simplified formula: D equals aM, in which D stands for dioptric power as determined by the first focal length; a stands for the index (relative index)
PASCAL JI. NEW CONCEPTION OF DIOPTRIC POWER. Arch Ophthalmol. 1933;9(2):244–247. doi:10.1001/archopht.1933.00830010257007
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