Evaluation of the International Standards Organisation/Draft International Standard model eye for use with automated infra-red optometers

A recent Draft International Standard describes a method for establishing the accuracy of automated infra-red optometers, using model eyes. In the present study we evaluate the performance of a series of automated infra-red optometers using model eyes constructed to the specifications of the Draft International Standard. The results demonstrate systematic differences between the values predicted by calculation from the standard and those found by measurement. These differences were reduced but not eliminated when the effects of non-paraxial refraction through the limiting aperture of the model eyes was taken into account. We conclude that the formula used to predict values of refractive power from the Draft International Standard is inappropriate because it fails to account for higher order aberrations.