Visual acuity and blur: An extended depth-of-focus model.

PURPOSE

This article proposes a simple model that describes the quantitative relationship between visual acuity and defocus (as in defocus curves) in the presence of higher-order aberrations (HOA).

METHODS

The basis model for describing the relationship between visual acuity and blur was taken from Blendowske as a starting point to develop an extended model applicable to defocus curves. The basis of Blendowskes's data is extended by incorporating effects induced by HOA. Aberrometric refractive errors are transformed into a single blur quantity b, also termed dioptric distance, which serves as an input in both models. The possible influence of the axes of asymmetric aberrations and the pupil size is not included.

RESULTS

The extended model has been used to generate reference data for a bi-aspheric multifocal correction profile for presbyopia. It provides reference data similar to what has been reported in the literature for that particular profile.

CONCLUSIONS

The model proposed in this article can be used to determine depth-of-focus effects associated with the presence of HOA. The extended model seems to provide a valid description for defocus curves. Actual uncertainties in experimental data on unaided visual acuity, especially the frequent lack of information on pupil diameter, prevent meaningful numerical comparison and the refinement of both models. However, theoretical arguments are provided in support of the extended model.