Predicting clinical visual acuity of presbyopia treatments

PURPOSE: To predict the potential clinical visual acuity of different presbyopia treatments. METHODS: The defocus transfer function (DTF) is a mathematical technique for simultaneously illustrating the optical transfer function for all levels of defocus. Through-focus clinical visual acuity measurements were superimposed onto the DTF to determine the corresponding retinal contrast and map out a modulation threshold curve. The process is performed for an apodized diffractive and a zonal refractive intraocular lens, as well as an opaque annular ring implant that extends depth of focus. RESULTS: Clinical visual acuity measurements appear to track contours on the DTF. The elevation of these contours changes as a function of spatial frequency, with the general trend being that for higher spatial frequencies, more retinal contrast is needed to achieve a given level of visual acuity. The presence of these contours suggests a minimum level of retinal contrast is needed to achieve a given visual acuity, and if this threshold is exceeded, the presbyopia treatment can provide the corresponding acuity clinically. CONCLUSIONS: The DTF provides a global view of ocular performance for all object distances. The disparate technologies investigated all gave similar modulation threshold curves. These results suggest that the modulation threshold curve can be used to predict potential visual acuity of other multifocal lens designs and methods for treating presbyopia.