COMPARISON OF 3 METHODS OF ESTIMATING THE PARAMETERS OF THE NAKA-RUSHTON EQUATION

The Naka-Rushton equation empirically describes the amplitude R of the dark-adapted electroretinogram b-wave, as a function of stimulus lumi nance L, as R/R(max) = L(n)/(L(n) + K(n)). Estimating the three parame ters R(max), n, and K of this function from electroretinogram data is of both experimental and clinical interest. Several different approach es have been developed to accomplish this analysis, but these approach es may derive different estimates of the three parameters. To examine this possibility, we compared the results of three methods of fitting the Naka-Rushton equation to data sets obtained from 30 normal subject s. Two methods were nonlinear curve-fitting programs; the third method involved fitting a regression line to transformed data. The results i ndicate that solutions provided by these methods have consistent diffe rences, which may be an important consideration when comparing results reported in studies that used different curve-fitting methods.