Comparing methods to estimate the human lens power.

UNLABELLED PURPOSE. To compare the accuracy of different methods of calculating human lens power when lens thickness is not available. METHODS. Lens power was calculated by four METHODS Three methods were used with previously published biometry and refraction data of 184 emmetropic and myopic eyes of 184 subjects (age range, 18-63 years; spherical equivalent range, -12.38 to +0.75 D). These three methods consist of the Bennett method, which uses lens thickness, a modification of the Stenström method and the Bennett-Rabbetts method, both of which do not require knowledge of lens thickness. These methods include c constants, which represent distances from lens surfaces to principal planes. Lens powers calculated with these methods were compared with those calculated using phakometry data available for a subgroup of 66 emmetropic eyes (66 subjects). RESULTS. Lens powers obtained from the Bennett method corresponded well with those obtained by phakometry for emmetropic eyes, although individual differences up to 3.5 D occurred. Lens powers obtained from the modified-Stenström and Bennett-Rabbetts methods deviated significantly from those obtained with either the Bennett method or phakometry. Customizing the c constants improved this agreement, but applying these constants to the entire group gave mean lens power differences of 0.71 ± 0.56 D compared with the Bennett method: By further optimizing the c constants, the agreement with the Bennett method was within ±1 D for 95% of the eyes. CONCLUSIONS. With appropriate constants, the modified Stenström and Bennett-Rabbetts methods provide a good approximation of the Bennett lens power in emmetropic and myopic eyes.