[Theoretical formulas for the power of artificial lenses]

After having recalled the principles of lens power calculation, we analyse in detail the parameters of the (Formula: see text). Corneal power K read on keratometers has to be modified, for it is about one diopter too strong. Evaluation of the anterior chamber depth C is analysed and corrected of 0.08 mm for the 1st C and of 0.06 mm for the 2nd C. Ultrasonic axial length L should be increased by the retinal thickness; the error induced by neglecting this correction is concealed by the overestimation of K in usual formulas. The equivalent power of the lens De is slightly underestimated relative to back surface power supplied by the manufacturer. The various formulas available in the Literature are commented and compared. A new formula is proposed, which is more particularly adapted to contact ultrasound probes, such as Digiecho II, which seem to under-evaluate L and C values.