Posterior chamber lens implantation is increasingly employed in the management of paediatric cataract, sometimes in infants within a few weeks of birth. The need to implant a lens of fixed power into an eye that is still growing creates a problem—what power lens should be selected? This is especially a dilemma in infants under 18 months of age, the period of most rapid postnatal ocular growth, during which there can be a substantial myopic shift. Using hand held instruments, reliable keratometry and axial length measurements can be obtained in children, and implant power calculations using adult formulas are accurate in the paediatric eye.1 However, implanting a lens at the calculated power risks significant myopia at ocular maturity. The paediatric cataract surgeon therefore now requires an additional “formula”, one that will predict the final refraction for any selected lens on the basis of the patient’s age. An initial …