Embodiments of the present invention provide a computer-implemented method of determining a parameter indicative of dark adaptation of an eye, comprising receiving threshold data from a dark adaptometer indicative of a perception threshold of the eye, fitting first and second models to the threshold data, wherein the first model is associated with a first dark adaptation mechanism and the second model is associated with the first dark adaption mechanism and a second dark adaptation mechanism, determining a confidence associated with the fitting of each of the first and second models to the received threshold data, iteratively repeating the steps of receiving the threshold data and fitting the first and second models in dependence on the determined confidence, and outputting an indication of one or more parameters indicative of dark adaptation of an eye associated with one or both of the first and second models.